Maybe this is the problem... IMO, "fiat" is not a "system". It's the lack of a system. So if a game presents a system and says you don't have to use it, you can use fiat... that's disregarding the system which can be done with or without explicit advice from the rules.
So, since most games say to make NPCs, just assign whatever stats & skills feel right, that means most games have "systemless" NPC creation?
