I've been giving a bit more thought to how Sorcerer can interact with the DPS/Tank/Healer split I think it's actually probably better for Dark Magic to be the tank line and Daedric Summoning be the healer/buffer line.

Swap Bound Armor and Conjured Ward into Dark Magic, replace them with Daedric Mines and Dark Exchange. Put the heal back on Ward so it can be a self heal for sorc tanks.

Make Exchange a group skill that sacs caster health for some kind of group buff which includes the owner's pets.

That would give the summoning line the group heal, group ward, and group buff options, and make grouping with it as a healer feel like an extension of its solo identity.

Yeah Swallow Soul is quite fair in comparison to other ranged instant spammables. I'd probably just add a small thematic buff like "this ability always applies the Hemorrhage status effect on hit" to make it feel more blood magic related which would add a decent amount of DPS, but not put the skill over a crazy budget, and then focus on the passives and making the dot/ult more worth using for damage dealers.

As discussed in skinny's stream when going over how to better incentivise mixed damage/utility lines like this after subclassing, a great suggestion I saw was change the 3% healing done per slotted passive into 2% healing and damage done, but from both bars.

So in a situation where you have 3 front, 1 back for example, previously you'd get 9% and 3% healing done respectively, but the new version would give 8% for both bars all the time. While I don't think this would replace Assassination as the go to NB damage dealing line, it would be of great use for solo/PvP/and pure classes with the 6% resources and ult gen, as a hybrid line, avoiding completely gutting yourself for not using Assassination instead.

Also, off topicish, but on the subject of pure classing and making these odd lines usable again, I think ZOS should look to how Sorc's function. The Storm Calling line's 108 ws damage for slotting works for all skill lines, what if Assassination's did the same for the 2.5% Crit chance? Obviously that's very strong, but technically the 108 vs 2.5% is equal to the ratio we find from sets of 129 vs 3%. I think it's just worth considering some version of this because it does make taking 2-3 lines for Sorc more enticing than other classes have it, the main problem right now is Dark Magic/Daedric Summoning just kinda suck, but that passive is really well designed imp.

My only gripe with that idea is that Storm Calling becomes this base must have line. If you want Daedric Summoning, you want Storm Calling so those skills mean something per slotted. Same goes if you wanted only Dark Magic, you should probably take Storm Calling too. Maybe this wouldn't be an issue with Siphoning and a rework to the healing done passive as discussed above.. but why not something completely new instead like...

Move the 108 ws damage per slotted for Storm Calling into a new passive tree that applies any time you take ANY Sorc line. Maybe move some other passives in there. Consider adding the classes minor group buff too. This way someone could take Daedric Summoning without Storm Calling or Dark Magic, and still get 108 ws damage per slotted, 10% of your main resource, and Minor Prophecy for example.

Templar could give 2% ws damage and armor per Templar skill slotted, minor Sorcery, and -5% resource/ult cost, etc. Add something new in the places these passives were taken from.

Unless they did this for all classes at the same time, it wouldn't really work given the current context of the game, but I think it would be an interesting way to promote subclassing and pureclassing, rather than what is now where lines are just completely killed off or made redundant for the majority of content.