Aside from Winter's Embrace, only Herald of the Tome and Grave Lord have one or two Frost abilities. If you include Ice Staves, you might be able to squeeze out a Frost theme, but Ice Staves' passive isn't great, and choosing an entire skill line for a single ability seems disproportionate. Furthermore, Herald of the Tome and Grave Lord each have unique mechanics, like Crux and corpses, so they might not necessarily fit the Frost theme.
I think the Frost theme should prioritize reworking Winter's Embrace's active ability and Ice Staves' passive. The two morph functions of Frozen Gate and Frost Cloak are too similar, so perhaps one of them could be redesigned into a PVE damage version.
For example:
The original function of Expansive Frost Cloak was merged into Ice Fortress, and Expansive Frost Cloak was redesigned to make it a useful PVE damage option, such as "No longer grants Major Resolve, but when you deal direct damage with Frost, you deal an additional Frost damage to the first target hit and all targets within 8 feet of it for 30 seconds."

Which merges Frozen Device with Frozen Retreat and redesigns Frozen Device to "Summon an ancient portal, causing frost damage to the designated area and summoning a Frost Atronach for 30 seconds. The Frost Atronach attacks once every 2 seconds, dealing frost damage to a 7-foot fan in front of you."

And Ice Staves' passive can be used to Knowledge adds new Ice Staff abilities. For example, equipping an Ice Staff increases your damage to monsters by 12%.

These changes have minimal impact on PvP, as the most commonly used Frost damage in PvP is mostly dot damage, such as Arctic Blast and Northern Storm. This will increase Frost-themed area damage, but since the current top-tier Fatecarver builds rarely utilize Frost damage, it won't make Fatecarver-related builds any stronger.

NB's Shadowy Disguise was the first skill in the entire class skill line to provide increased monster damage. We had expected this to be extended to more skill lines in the future, but disappointingly, this hasn't happened. However, this concept is undoubtedly the simplest way to differentiate between PvP and PvE. While Shadowy Disguise will lose Major Prophecy and Major Savagery in U47, its increased monster damage will remain. I think Shadowy Disguise needs a bit of a buff to make the stealth/shadow theme playable. Increasing the buff duration from 10 seconds to 20 seconds and increasing the monster damage to 12% will make it more appealing and easier to weave with other skills. Also, since Fatecarver-related builds use Banner Bearer, these builds will be unable to use Shadowy Disguise while Banner Bearer is active, so it won't buff Fatecarver. Other Shadow lane abilities could benefit from some adjustments, such as increasing Twisting Path's damage, merging Mass Hysteria with Manifestation of Terror, and reworking Manifestation of Terror to add a 20-second Dot, allowing it to play a better role in PvE. There are many ways to remove negative effects in PvP now, so it won't have a significant impact there.

The area and damage caused by Veil of Blades need to be increased, and it provides Major Force to the team after enabling synergy, which should make it more popular in PvE groups.

Since Shadow lane damage is already low, increasing its area damage won't make Fatecarver-related builds any stronger.

Shock Damage has just as few skill sources as the Frost theme, and its passive is the weakest. Flame has DK's World in Ruin and Combustion, Frost has Glacial Presence and Piercing Cold, and Shock only has Energized.

Also, like the Frost theme, Shock Damage's primary source is the Storm Calling tier, and its skill morphs differ little. However, since Streak is indeed very strong in PvP, improving the Shock theme has always been a thorny issue.

I think the simplest approach is to introduce a damage increase to monsters, similar to Shadowy Disguise, and buff some less-used skills. For example, Endless Fury has been reworked, with the following example: "Throws a bolt of lightning at the target. Each hit applies a stack of 'Electric Shock' to the target and increases your damage to monsters by 3% for 10 seconds, up to a maximum of 3 stacks. When 3 stacks of 'Electric Shock' are reached, it deals Shock Damage to the target and all targets within 8 feet. While slotted on either ability bar, gains Major Brutality and Major Sorcery." Because it encourages the use of skills to stack debuffs, it clashes with the style of Fatecarver-related builds and will not enhance Fatecarver-related builds, but it will still enhance Shock-themed area damage.

Power Surge and Critical Surge are in a similar situation to Expansive Frost Cloak & Ice Fortress: their morphs are too similar and should be merged. For example, "When you deal critical damage or critical healing, heal yourself and nearby targets, up to once every 1 second. While slotted on either bar, you gain Major Prophecy and Savagery." Another morph could be more damage-focused, for example: "When you deal damage with Sorc skills, you inflict Shock Damage to the target, up to once every 3 seconds, and this damage always adds Concussed. While slotted on either bar, you gain Major Prophecy and Savagery."

Since Sorc skills are required to trigger, they also won't enhance Fatecarver-related builds.

The biggest problem with Necromancer Theme is that the corpse mechanic can be a bit annoying at times, and there's a limit on how many corpses there are. But overall, the Necromancer Theme's mechanics are more complete. Furthermore, after Fatecarver became a direct damage modifier, most of the Necromancer Theme's active skills have little impact on Fatecarver-related builds. Therefore, slightly buffing the Necromancer Theme's skills likely won't benefit Fatecarver-related builds. Grave Lord's Sacrifice is currently one of the less popular skills in the Necromancer Theme, but I think it could benefit from a buff, such as "While slotted (or active), increases area damage by 5%." A 5% damage buff is the same as Solar Barrage, so it shouldn't increase Fatecarver's damage compared to the existing Arc/NB/Temple combo.

Also, the effects of Unnerving Boneyard and Avid Boneyard could be merged, with Unnerving Boneyard redesigned to something like "Spend a stam to desecrate the ground within 15 feet of you for 5 seconds, dealing x points of disease damage every 1 second. Each corpse consumed increases this duration by 5 seconds based on the number of corpses consumed within 15 feet, up to a maximum of 20 seconds." Since maxing this skill requires 3 corpses, this would encourage Necromancer Theme players to use Venom/Ricochet Skull, Blastbones/GLS, Skeletal Archer/Skeletal Arcanist, and Necro Class Mastery. This also clashes with Fatecarver-related builds, as corpses must be constantly created to maximize area-of-effect damage, and without creating corpses, the 5-second duration makes it difficult to weave in with Fatecarver.

Dark Mage, similar to the Shadow theme, offers a variety of abilities within the main Dark Magic line, including healing, tanking, damage, and utility. However, this lack of refinement puts the line in an awkward position in the era of subclassing.
However, the increased maximum resource in U47 doesn't improve Dark Magic's current state. Both Dark Magic's active and passive abilities require further rework and adjustments to be effective in PvE and not out of control in PvP. For example, to avoid being too similar to Hemorrhage, but still be able to compete with it, you can add "increase direct damage caused by 6%" to Exploitation. 6% direct damage isn't a particularly high buff, although it may enhance Fatecarver, but considering that many people already have 5% class damage from Solar Barrage, it's still reasonable to let Exploitation provide 6% direct damage. If you're worried about direct damage making the Crystal uncontrollable in PvP, perhaps as a balance, you could slightly reduce the Crystal's damage by 2-3%. This will only increase the Crystal's damage by around 3%, and due to its unstable proc chance, it shouldn't make it any more threatening in PvP.

Next is Shattering Spines. After the last update, Shattering Spines remains underused because its damage is too low in PvE and it doesn't work well with other skills. Adding a 10/15/20-second dot to it would make it worthwhile to add to your damage rotation. Blood Magic needs to have its critical damage and critical treatment increased by 8%. Currently, U47's maximum resource doesn't make Blood Magic more popular.

The damage caused by Suppression Field should be increased. To balance this, the effects of Silence and Stun could be removed, and Major Brittle could be added to the damaged target instead. This will compete with other damage-type ultimate skills.

Similar to Shadow, Dark Magic's damage is inherently low, so even increasing its damage won't make Fatecarver-related builds any stronger.

The Zoo Theme is primarily limited by the fact that pets primarily deal single-target damage, and even those with cleave abilities are generally weak. Furthermore, Daedric Summoning pets require 2-bar, significantly limiting the flexibility and options of related builds. Furthermore, the strongest area-of-effect pet is Blighted Blastbones from the Grave Lord line, but due to its short lifespan, it's sometimes not considered part of the Zoo Theme. Additionally, there are still a few situations in PvE where pets can die, and the 1.5-second cast time and high cost of Daedric Summoning pets make resummoning pets quite annoying.

However, the 2-bar limit prevents the Menagerie theme from overly empowering Fatecarver-related builds, so I think it's worth retaining the 2-bar limit while increasing the area damage dealt by pets.

For example: When Twilight Tormentor uses her active ability, the effect could be changed to "Increases Tormentor's damage by 15%, and each attack deals damage to the target and enemies within 8 feet for 20 seconds." This would make using pets' active abilities more appealing. Furthermore, Eternal Guardian and Wild Guardian could be merged, with Wild Guardian redesigned to, for example, "Summons a Frost Troll that deals Frost damage to the Cone area in front of it every 2 seconds. When using an active skill, each attack deals 5% increased damage and always inflicts Chilled for 10 seconds." This should benefit pure Wardens, Frost themes, and Zoo themes simultaneously, providing another reliable source of area damage. Pets are also relatively ineffective in PVP, so there's no need to worry about them impacting PVP.

Disease Theme also has a relatively limited skill source, and its abilities are spread across multiple skill lines. This is why players have been calling for a dedicated skill line dedicated to the disease theme. Currently, the main sources of disease damage are Blighted Blastbones, Detonating Siphon, Death Stroke (with morph), Killer's Blade, Relentless Focus, Power Extraction, and Pestilent Colossus, totaling three skill lines. Assassination is already quite good, and Blighted Blastbones already offers strong area-of-effect damage, so we'll skip those for now. This section will focus on Detonating Siphon and Power Extraction.

Detonating Siphon's biggest drawback is its corpse mechanics, and its effects are too similar to Mystic Siphon's. Overall, however, Detonating Siphon's damage is decent, and it also has an additional 3% damage buff. Therefore, I recommend slightly increasing its range from 5 feet to 6 or 7 feet, making it easier to hit nearby targets.

Power Extraction, on the other hand, suffers from insufficient damage, requiring an enemy to hit for Major Brutality and Sorcery to take effect, and its effects are too similar to Sap Essence. I recommend reworking them to differentiate them. For example, Major Brutality and Sorcery has been changed to work with 2 bars once slotted, making Power Extraction a viable mid-range spam, and Sap Essence has been merged with the old Power Extraction. For example, "Power Extraction now consumes Stamina, deals disease damage to a target within 15 feet and enemies within 8 feet of it, and adds Minor Cowardice to them for 10 seconds. This skill has a higher chance to inflict Diseased. Gain Major Brutality and Sorcery after slotting any bar." Sap Essence has been changed to "Deal magic damage to nearby enemies, healing you and allies. When you hit an enemy, you gain Minor Courage, and each enemy hit increases the healing by 20%. Gain Major Brutality and Sorcery after slotting any bar."
Alternatively, Swallow Soul could be reworked, changing its damage to disease and slightly increasing it, and causing disease damage to enemies within 8 feet of the player once the healing effect ends, which should make it a suitable addition to the damage rotation. Since disease status effects have their own area damage, this should also slightly increase pure NB area damage. Furthermore, since disease-type spam is available, and since most Syphon lines' abilities don't buff Fatecarver-related builds, and since you can't run two NB lines unless you're a primary NB, there's no need to worry about this change buffing Fatecarver-related builds.