I can't tell if this is actually a bug or not, but it seems that Looting has little to no effect. I'm using Tinkers, and to some extent, it has worked. But a lot of the "rare" drops aren't effected. Even rare vanilla drops are affected. Those aren't, which makes it literally impossible to get any of the important items you want

The loot is coded in a way where what a gaia mobs drops is hardcoded. No matter if you got looting or not.