He was a bad ass who could whoop just about anyone walking the planet (including Chuck "My Beard Looks Like Pubic Hair" Norris), despite being half their size. I have doubts if there's even anyone that's alive today that could take him. He's also seems to be a pretty wise and intelligent man, but being Chinese, I guess that's to be expected.
He was also blessed enough to die in his prime (as odd as they may sound to most of you.)
Chuck was a legit competitor in full contact karate plus holds Black Belts in Judo and BJJ plus a big background in Tae Kwon Doe, Bruce never competed in any sanctioned fights I believe. There are rumours of unsanctioned fights sure but no proof, even if they did happen they'd have been firstly exaggerated and secondly likely against untrained guys.
Bruce Lee is an inspiration for most but people seem to forget he was an actor first and and an untested martial artists second. His hand speed would have caused trouble for some guys but could he grapple? Can he stop someone dumping him on his head? He semmed to have trained with Lebell but is that enough against life time competitors?
Here is Daniel Cormier, a US Olympian in Freestyle wrestling throwing Dan Henderson another Olympian in Greco Roman wrestling. Hendo is old sure but his pedigree is a lot better than Lee's. Imagine Bruce trying to throw a kick against this guy? DC would catch at least one leg. Hendo was 199 for this fight with DC around 215 / 220. Both are giants compared to Bruce.
We can even include guys around Bruce's size such as Mighty Mouse, who again is an accomplished amateur wrestler.
The early UFC events showed us pure grappling > pure striking as you can dictate where the fight takes place. Royce won the first 3 of 4 events proving this principle. Bruce had the mentality of combining all Arts so could have done well as an MMA fighter but his skillset had major flaws he needed to address. If any of the old guys had the best chance of beating modern guys prime for prime it's Judo Gene Lebell with his background in Judo and Catch Wrestling.
Finally D'Z is right weight classes do exist for a reason, skill can beat size (see Royce vs Severn) but there is a level where the size is too much of an advantage and the skill difference is too small.