well, having studied Bruce's Art for years I can tell you that JKD is very effective in any fighting situation. and Mr. Lee was the best.
extreme power, speed, timing ect ect., He looked way different in actual combat than in his movies, straightblasting his opponent to the ground ect. He would have beat many of the greats and at his prime. I would probably say that he would get several crowns. He also would have incorporated more grappling into JKD as us JKDC practitioners have.
In the UFC ring it still does not mimic actual combat on the street where things such as Bui Jee (eye strikes) and other devistating techniques cannot be used.
JKD has strong ties to wing chun and it's simplicity and centerline attack ect.
Well, I could go on and on
there is alot of good fighters out there
and each have their time to shine, Bruce Lee had his.
Who's to say, he's gone but left a great legacy! JKD