If there are really just a few, it could be explained by chance. Warren Buffet is often cited in that group and yet, a blindfolded monkey would have done better than him in the past 20 years[0].
Warren Buffet also said 20 years ago that he was having trouble find any stocks that he wanted to buy, so he predicted his poor performance. He did very well for the first 30 years of his investment life.
I could be wrong but I don't believe Renaissance Technologies makes their money picking individual stocks. My understanding is that they mostly make money with (statistical) arbitrage, market making, etc.
[0] https://www.linkedin.com/pulse/warren-buffett-has-underperfo...