Why is the healer class basically a one spell dps class?

[Anhra]

Blue mage is absurdly broken. If it was 80, it would annihilate savages, trivializing them. Imagine being able to diamondback any failed mechanic.

Diamond Back, Instant Death and certain other Skills aside, the way how Tank/Healer BLU plays like, is imo, how those two Roles should be like.

I am not suggesting the same Skills here to be inplimented into said healers/tanks, but the way how they interact with the party and enemies, as well as the way how Bosses do overall damage to then?

That would truly be a great way of kicking healers and tanks towards the right direction.