every exceptionally talented person/group is unlikely to show up in the exact circumstances that they do. In a thunderstorm, each individual tree has a very low chance of being struck by lightning, but nobody is surprised that some tree is struck by lightning.

Of course, to realize their potential they also had to work hard, and collaborating with other exceptionally talented artists also no doubt helped.

I would also push back on the idea that the music they created as a group was much better than what came after. George, in particular, released arguably his best work (all things must pass) after the breakup, and both john and paul released great albums afterward (imagine, ram)