I honestly have actually never been entirely certain if luck actually did anything besides screw up gae bolg and other similar phantasms or it worked more like DND luck.
Hmmm....well, musing out loud, given how all the other stats have turned out to be more basic and literal then we had thought, I am inclined to think the latter maybe.
Edit: FWIW saber's luck makes her an epic card shark, according to HA, so that lends credence to the idea.