I actually studied Gracie Jiu-jitsu for a time (many years ago) and I can tell you that in a fight between a grappler vs. any other fighting style, the grappler wins 99% of the time. Whatever the technique, very few disiplines that I am aware of teach you what to do once your on the ground.
I studied for a few years, but never lasted more than 10 seconds in fight with my teacher, even then he was probably toying with me.
Lee was never shown to be a grappler though. Jeet Kune Do, which calls itself the style of no style, does seem to focus more on striking though.
Oh and btw I think Bas Rhutten mentioned this once. There has been many internet discussion between who would win if bruce lee came back to life and fought this guy or that guy. On his first day back from the dead, even in peak physical condition with all his former prowess, bruce lee would probably lose in any professional fight.
But we are talking about the guy who pioneered martial arts, pioneered fitness, and pioneered the art of no style. Which is why Dana white calls him the father of MMA. A guy like Bruce would just establish and new training program, and come back extremely dangerous in the ring, able to stand toe to toe with anyone.
From a practical and technical standpoint the gracies would probably be a greater influence in MMA b/c they introduced grappling to the sport.