Sets
Sentiental (monster set)
Spell power cure is optimal, but you have options, but I won't suggest using worm it's over kill for the class.

I am going to assume overall PvE content (4 man, vDSA, Trials) and I would highly suggest using 5x Spell Power Cure as your base set for pretty much all of the PvE content when possible. Worm or Infallible Aether (or Gossamer/Twilight depending on group and fight) should be your secondary sets. Aether is I think the best for 4 man and vDSA as consistent Minor Vulnerability is hard to come by.

Sentinel is a great set for stack fights, I would even recommend it on an offtank.

Bar 1
* Dark Exchange - self heals and proc to passive for spell critical %3
* Echoing vigor (alternatives: mutagen or rapid) healing over time (it's stamina, but heals the pet and it's a 7k healing over time which is faster to case to mutiple people in trials)
*Summoned Winged Twilight - The most powerful Burst heal in game and slight dps that might proc implosion
* Combat prayer (alternative bless of protection (easier to get wards on people)) - buffs for damge and resstiance
* Emprowered ward (why mages love us more then say... ..) - 10%magick regain to all allies
* Ult Absporbtion field

I see no need at all for Dark Exchange for a Sorc in a Trial setting. Maybe 4 man but not a Trial setting. Healing Springs would return enough magicka back to you. Heavy attacks with restoration staff occasionally work fine as well if you really need magicka back. If all else fails, use a potion.

I see no need at all for Echoing Vigor as a Magicka-based healer. Unless you want to spec your CP and such towards getting more effective Vigors out, I see no point to it if you're a MagSorc. I would probably not run Mutagen/Rapid in most of the current 12-man content. Depends on the fight. For vDSA and such, for sure it is useful to keep up those heal over times while keeping SPC on others.

Summoned Winged Twilight can both be a blessing and burden. It can take away a SPC buff since it is considered an ally so one person could be missing out on it (SPC has a 6 person limit) but should be fine in a 4 man. I would argue this skill, while definitely better than what it was, is not the most powerful burst heal in the game. The Templar's Breath of Life with Major Mending up definitely heals for more. Furthermore BoL does not require a pet to be double-slotted on both bars and pets do die.

Combat Prayer is good and pretty much a must for that Minor Berserk for group buff. Also the 10% magicka regen from Empowered Ward is pretty much almost insignificant for magicka DPS that usually have 600-700 magicka recovery.

Another thing that sets Templars (or even Nightblade healers) apart from the rest is the lack of damage mitigation offered to a group when needed. Solar Prison (Templar) can be placed on target and people don't have to stack on a certain spot as the damage reduction applies to targets. Veil (Nightblade) can be placed on ground but people have to stack and it's sort of a different buff but damage mitigation nonetheless. The Sorc's Negate (or DK's Magma Shell) that comes closest to that kind of stuff does not really offer mitigation but maybe some more healing.

Furthermore just having a non-Templar healer tagging along with a Templar healer can actually put some burden on the Templar healer as that healer needs to rotate more shards in, save a nova, etc.

I can only really think of two fights in Trial content and one fight in vDSA that would perfectly accommodate a Negate whereas a Nova or even Veil is applicable to pretty much every fight.

Bar
* Mystic orbs ( why mages should want sorcs) - you can spam these and still have more over
* Healing Springs - saves magicka
* Summoned Winged Twilight - Heals it's self and two others great when you are moving around
* Circle of Protection - 8% Damage migration and 10% stamina gain (developers you see please make the circle bigger for us... it's rough being us, but it could be better)
Overflowing Altar - at the right moment this damage migration also a long last standing heal for general hugging moments with you group members
* Revining Barriar (alt war horn) - give allies a ward but what you like is the extra 30k+ regain over time, so hp management along with magicka aid for your regain

I didn't quite understand what you meant by Sorcs being able to spam Mystic Orbs as any other class can do it as well. Healing Springs is good. Sometimes you want Illustrous Healing depending on fight/group. Again that pet being double-slotted hinders you somewhat but not much to do with a Sorc healer.

Altar does not provide any damage mitigation. It simply offers lifesteal for those standing in it. It's an underestimated skill to be sure.

I noticed you're missing Elemental Drain or Spirit Siphon. You should probably slot at least one of those for a Trial as it helps sustain and keeps up your SPC up (Spirit Siphon counts as you healing people when they're hitting affected target). No need to run both as the other healer usually runs one or the other. For 4-man, you want Elemental Drain. You can try to run both for 4-man but it can prove to be uncomfortable.

Personally I think your best options for ultimates as a Sorc healer in general is Aggressive Warhorn + Negate. Barrier sadly only hits up to 6 targets including yourself and is a bit weak against the damage that a group can experience sometimes in Trial content. It can be a clutch lifesaver but other than that, it offers no damage buff or real damage mitigation for the group which can save the fight.

What this build does
Unorthodox damage migration
10% magicka regain
10% stamina regain
4k stamina to multiple allies ... a lot in trial as you are usually close to each other.
Powerful heals

Unorthodox to be sure, effective perhaps but the best? Sadly not. Sorcerers, Nightblades and Dragonknights come nowhere close yet to a Magplar healer in terms of heals, group utility and adaptability to a lot of situations.

But if you're not looking to min-max and if you're not looking to optimize, then this is fine. But if you're expecting to do smoothly and aim for high scores (it's possible but unnecessarily harder), I'm just going to tell you what a lot of Trial groups would probably say: "Make a Templar".