Well I went out to test it.
At first I tested 24+ magic potency (as only change). No difference in damage.
Then I made a Circlet to test if elemental potency would have any benefit. 9+ Fire magic potency (as only change). No difference in damage.

Conclusion:
Magic potency and Elemental potency makes no difference as of right now. However, we can attach elemental potency materia to PGL weapons so this makes me think its suppose to still and needs to be fixed.

Side note:
I did not do an extremely long test on this. There may be an extremely low benefit but it is certainly low enough to not even consider gearing up for it.