Better ideas: class uses items and turns a hidden materia slot into a guaranteed materia slot (lessening RNG at the cost of crafting mats). Higher class gets, access to high guaranteed slots (up to 5).
At max level, adds another Hidden slot to an item.

Then for other facets of the class, we can use an already brought facet of the game into DoL - Scrolls. Scrolls would act like pots, on seperate timer.
We could also add a static Materia Infusion Scroll slot - Like the Relic, but static on your inventory. A new slow really - also somewhere to dump materia for faster churn, and giving a way to min/max for the stats/build you want.

We don't want to invalidate other crafting classes, but we'd be better synergizing with them.