General Community Resistant to Healer Damage?

[Lilseph]

What if it necessitated regen AND Cure II spam?
You know, if autohits were actually a threat to the tank?

Then that falls under the latter. Too MP costly to actually be sustainable with the current battle system. This also feeds into the next point:

Some leveling dungeons feel that way, undergeared tanks in there are more interesting to heal than tanks in savage raids. Mobs hit like 40t trucks!
Why can't we have that in expert dungeons? Why do they have to be so easy, just so a few returnees can catch up?

Player progression balance. Levelling dungeons hit extremely hard because they need to scale them to fit player progression but also be balanced for players at the max ilvl cap for the previous expansion. You also don't have all your tools, so it's significantly more challenging. Expert Dungeons have to follow this rule too. They technically can set the difficulty higher and raise the minimum ilvl requirement, but how are players who are playing catch up going to unlock the more lucrative dungeons set at i530 when the only gear they have access to are i430 dungeon gear and old dungeons that give a paltry sum of 45 tomes per clear?

As for the mana thing: you do realize that is just a balancing numbers game. Easy to fix. Very easy.

Nope. Reducing MP costs across the board means access to more MP for Healers. Every encounter would have to be adjusted to accommodate this because you're essentially giving healers nigh infinite mp if not careful.