Materia - Multi meld swapping.

[Rongway]

Or they could make DH a DPS only stat so WAR is the only one who can use it through Inner Release. Problem solved.

WAR attacks wouldn't need to be a special case of direct hit applying to a non-DPS job. All dhits do is increase damage by a flat 25%, so just make Inner Release increase damage by 25% and guarantee crits and it wouldn't need to dhit at all.

[Garnix]

Remove materia melding from the game. Problem solved.

EDIT: Honestly...half joking there. They could make a system similar to how we can adjust our stats on relic weapons.
Instead of having dozens of different materia just have a "Combat materia rank 9/10". Meld that, and then you can adjust at will.
And apply that to crafters as well, so you just have to overmeld without worrying about what stat you overmeld.