What even is the purpose of all those non melee/blm jobs?

[Valence]

No no, do not bring that difficulty stuff into this thread too.
It is about consistency, not difficulty. They have some connection to each other but are not directly causal.
I think Bard is harder to play at full throttle than Dragoon, but you still regulate both based on their damage consistency, not their difficulty.
Consistency of damage is decided by encounter design.

Because the charts somehow tend to prove your point? Last I checked at lower percentiles, not much seems to change. I'm not so sure about that consistency vs difficulty idea tbh.