DPS display could easily be solved with a system already in game.

[Zaft]

I don't understand the "DPS optimization doesn't matter outside of raid settings" argument at all. No one says it's okay for a tank to not be able to hold hate or to take the boss for a walk in low-level content. No one says it's okay for a healer to not Protect/Stoneskin or not heal effectively in low-level content.

A DPS' job is to deal damage. If they are not doing damage appropriate to the level of gear they are wearing, they are not doing their job. Period.

Why is this considered acceptable?

Because we can't have anybody with hurt feelings.