Class Passives and Scribing
In order to bring more power to "pure" classes, passives should only activate if the player is using the respective class. Scripts should only be available to players that do not borrow skill lines from other classes. For example, if I am a Dragonknight, I should only benefit from DK passives. I should not be getting the crit chance from the Master Assassin passive in the Nightblade's Assassination skill line. Same goes for Class Scripts, as a DK I should only be able to use my Class Script if I have three DK skill lines. Subclassing and Scribing were introduced to help classes that lacked viable skills or passives and allow them to borrow from other classes. This works, but the classes that already had everything are borrowing abilities and passives that gives rise to god-like builds that should have never existed. This allows players to stack crit chance or crit damage beyond the inteded limit, hence the current crit meta. I would even go as far as to suggest that Scribing should not be available to subclassers as it was, once again, intended to provide pure classes a way to acquire missing buffs and debuffs, which was then replaced by Subclassing. Scribing should be the alternative to players that decide to stay a pure class and do not want to suffer possible penalties or miss out on crucial class passives/skills. This will also greatly help with future balance because if a class needs a passive changed it will not affect other classes, regardless if they use the skill line.

Crit Chance and Crit Damage:
It's too high. Subclassing and Scribing made it too easy to stack crit chance and crit damage, limiting the viability of skill lines that don't boost these stats. It is no surprise that Animal Companions, Assassination, Aedric Spear and Grave Lord are some of the most popular skill lines, and of course Storm Calling.

Mythics:
These are too damn strong. We went from Spaulders of Ruin, which grant 260 weapon/spell damage to allies to Monomyth Reforged, which grants 20% crit damage. How did we get here? New mythics also seem to lack the drawbacks that their earlier counterparts had. Sea Serpent's coil has a 40% self snare. Thrassian Stranglers has a massive hit on resources and HP. Monomyth Reforged has Minor Vulnerability, which is common in PvP environments anyway, so players suffer no repercussions. Torc of the Last Ayleid King has no penalties. Being unable to benefit from other item set bonuses is not a big enough penalty.

Class Buffs and Bonuses:
Skills that boost healing and damage should only work for skills belonging to that class, like Sacrificial Bones. Skills like Solar Flare should only buff Templar skills. Passives should obey this rule as well. An example: the Templar's Piercing Spear passive should only work with Templar skills.

Warden:
Deep Fissure should only apply Major and Minor Breach on the 3-second volley and not on the 9-second volley. This will prevent Wardens from preparing their assault from a safe distance, and would instead require them to be in close range where people can engage accordingly. This change will not affect the duration of the debuffs but it will limit the burst potential by a critical amount for Wardens. Warden is a melee class and should be punished for being at range.

Miscellaneous:
Players should have the option to apply skill styles to the entire skill toolkit while keeping the option to style each individual skill to their liking. This means all skills should be modifiable and styles should unlock for all skills. For example, as a DK, if I unlock the Ice Blue style, it should become available to all my skills, not just Lava Whip and Fiery Breath. This will give players the option of styling their entire toolkit while being able to style each skill differently. It should work like the outfit station but for skills.