This is absolutely hilarious to me.
People complain at great length that crafting gear isn't worth the trouble compared to dungeon gear, and then once it IS made viable compared to end game gear or at least towards acquiring endgame gear, they complain that it's TOO good.
Crafting 4-star gear takes a lot of work and money. Throwing materia slots on coil gear would diminish the time, effort, and money crafters put in to making gear, as well as make taking crafts beyond 50 for the purposes of making things other than cosmetic gear and housing items completely pointless. This still wouldn't apply towards food and potions, but those two have always been an exception anyway.