Fuhrer Drumpf
Orange Belt
There will always be exceptions. There are people who, with little or no training, can play nearly any piano piece after a single hearing (with no sheet music). That is not an indicator that piano shouldn't take years to learn.
But let's go back and look at those two examples. How much did Kano train in those 10 years? And did he have exceptional teachers? And what was his movement like before he started that training?
Bruce Lee was physically exceptional, and exceptionally driven. There are also some who say some of his ideas of WC were underdeveloped.
Kano and Lee weren't the exceptions. (And Lee didn't get muscle until much later. He was still pretty skinny when he was in The Green Hornet.) I think there are many amazing martial artists with a lot of creative potential who just choose to continue in their tradition. I've met many myself, including my stepfather, who was my first martial arts teacher and an extraordinary talent in Shotokan.