For those who main/semi-main a DPS (e.g. DNC, RDM) but like Healers...

[Shurrikhan]

All the extra healing by Healer Jobs is, apparently, overkill and not needed.

Unless Healers having enough DPS to clear content despite their inclusion somehow makes them indistinguishable from DPS despite their comparative paucity of offensive actions, neither do Tanks' 2-4 self-heal make them Healers.

Or are you suddenly instead so satisfied with the game's low healing requirements that you'd happily conflate one role's being able to do a tenth of another's output with their being the same thing just because that particular ceiling is so low?

I think the biggest thing is it would mean changing the combat model and encounter design to be far less rigid.

You're advocating that a capacity be allocated, to any real significance in capacity or gameplay, to a single role. That's literally asking for more rigid role divisions and less flexibility in how a given party may deal with encounter design or what encounter design may in turn leverage from the party. You'd have a greater breadth of tools available to work with if you just didn't section off those capacities to a single role.

The problem is a lack of undermechanics and actions or interactions by which to leverage them, not the lack of a role that'd be purposely neutered outside of full parties.

Quelling Strikes, was it?)

No, Quelling Strikes was literally just Diversion before it was moved to a Role Action for all but Rangers (who instead got their Enmity drop attached to Refresh and Tactician). It was never akin to anything like Misdirection or Shadewalker, let alone any distinct "Puller"-role tool.