It's not just the output of their team; compared to people like Bellard (and John Carmack, Jeff Dean, Peter Norvig, ...), 99.99% of people are mediocre. Increasing the output of 100 mediocre people by 20%-30% is worth more than contributing one person's output, even if it's 10x or 20x.

And I would argue the difference between a mediocre manager and a good manager is more than that.