"It struck me recently how few of the most successful people I know are mean."
There's probably a disconnect between the most successful people pg knows personally, and the handful of tech CEO's you know only from reputation. I'm willing to bet not even pg knows (or knew) Steve Jobs, Bill Gates, and Larry Ellison personally. Who does he know?
"I only know people who work in certain fields: startup founders, programmers, professors."
There are hundreds of successful startup founders, and you can name seven mean ones over the course of almost 50 years. I'm sure if we worked together we could come up with a few more, but it's a small, countable number. Y Combinator probably funds around seven successful startups every year, and that's not even counting the programmers and professors. I'm willing to bet PG's experience outstrips anything that you or I know purely from reputation.
Plus, I think some of your examples actually support pg's argument. Take Uber, for instance. The technical implementation of Uber is trivial. What enables Uber to survive is their ability to pick and win political fights with the taxi cartels, which is exactly the kind of place where pg would expect mean people to succeed. Oracle and Microsoft won, not based on technical merit but based on enterprise sales and deal-making.