First, most of us Jun Fan Gung fu/JKD practitioners refer to Bruce as Sijo.
Second, Bruce had a set curriculum for what he taught; and while that curriculum has now changed over the years with his students, it was pretty well set by the LA Chinatown era.
Bruce Lee had plenty of street fights growing up, and there are plenty of anecdotal stories of him fighting other martial artists here the states, particularly Wong Jack Man which was the catalyst for his development of Jeet Kune Do.
On the set of "Enter the Dragon" he fought a challenge match that was seen by the entire crew, and was even captured on film but that film was later destroyed by Warner Bros. because they thought it had nothing to do with the film itself.
Another thing, Bruce also fought in a boxing championship while in high school growing up in Hong Kong, and he supposedly fought a Thai boxer in Thailand while shooting the Big Boss.
Bruce may not have killed anyone, but he certainly had experience to back up his fighting philosophy. Plus, much of the focus mitts, kicking shields, and protective equipment came Bruce and his group because they were the very few in the US doing any full contact at the time. Don't believe me, go ask Dan Inosanto and Jerry Poteet, they'll tell you how it was.
Most people bash Bruce because they are 100% ignorant of what he was doing back then. They see his movies, which he obviously modified his movements so they looked better on the screen, and think to themselves that was all there is. Bull****!
Go read his notes, and really take some time to think about what he was talking about. If you still don't get it, go out and train under some of his students. But don't be a god**** keyboard warrior, trashing someone who has been dead for almost 40 years.
Was Bruce Lee a grandmaster? I don't know, and don't really care, what I do is use his example and discover myself through martial arts whether it's hitting a heavy bag or full contact sparring.
Peace.