Just make Tenacity and Piety into Determination

Piety only works for Healers and Tenacity only works for tanks, they basically never get melded. I think it's worth while just making them the Tank and Healer version of Determination and have it scale similarly so it is used over Determination in those particular roles.

Determination - For everyone +dmg +healing
Tenacity- Only Tanks +dmg +healing +dmg reduction
Piety - Only Healers +dmg +healing +mp regen.

This way all the dps can still meld Det, but Tanks and Healers will just meld Tenacity and Piety in place of det, so those materia don't all just get melted and wasted. Pretext of course that it scales the same as DET so that the roles would actually be incentivized to use them.

Then make Critical Hit and Direct Hit into Determination as well, because it's superfluous to have 3 different variables that all just make damage go up.

I wouldn't be opposed to just just have a speed materia and a damage materia and call it a day, it really doesn't matter in the end anyways.

Counter idea: Make things hit harder and tenacity more potent.
Make it so it's almost impossible to prog without some.