Edit: As a concrete example, he grew up with Wing Chun. But he realized that the static stance was a huge detriment in real fights, so he took the boxing footwork from Ali, which was a lot of moving around and staying mobile and not standing in one spot.
Realistically, hybrid martial arts have been around for a long time. When I was a kid (long before the MMA hype train), I did Karate, but it also involved learning ~30 judo throws, a lot of jujitsu, as well as a wide variety of weapons (bo, nunchucku, kama, eiku, sai, tonfa) as all of the instructors also were black belts in some Okinawan weapons art. It was a lot of fun and better than any martial arts training I had previously (made the years I spent on Taekwondo feel embarrassing), but still nearly useless against a mediocre Muay Thai and BJJ fighter.
Problem back then was information. Pre internet and stuff happening really far away from each other (Brazil and Hong Kong/USA).
UFC and the internet really helped to spread information on what actually works to a much wider audience (and from there to a group of practitioners) and thus sped up the development of the techniques a lot.
UFC also made it possible to make a living from actually fighting instead of teaching others which is/was the “traditional” way of making money from martial arts which allows the fighters to fully concentrate on their own skills.
Apart from that, I do take issue with the for some reason increasingly popular notion of Bruce Lee's fighthing being some sort of proto-MMA. MMA is not just taking something from various sources and calling it "<first name>-fu" or "<first name> tang doo". The essence of (old school) MMA/Vale Tudo is about finding out what works and what doesn't through literal trial by combat, it's not about the mix and match aspect.
I honestly don't understand why you're so eager to criticize what he did when you don't seem to know much about what he actually did and what his thoughts were about martial arts.