I feel like "rare monsters that drop gear" is already covered, with things like Odin and Ixion. It's glamour rather than equipment, but that's what lasts in this game.
Even then, the system only works well for as long as they're current. Drumming up enough participants for the Couerlregina boss in Dravania is hard, on the rare occasion that the FATE is even on - and in a year of playing (and taking three characters through ARR) I have never ever seen or heard of the Behemoth spawning in Coerthas.
