A hallmark character trait of the best leaders is being genuinely happy when they're surpassed by former subordinates.
It takes an enormous amount of humility, self confidence, & borderline altruism. It goes against human nature, which is naturally hierarchical & ego driven. I've seen many high performing people who are unable to cope when this happens and devolve into destructive behavior: gate keeping, sabotaging, behaviors that leave behind collateral damage to themselves and often their entire firms.
The best leaders, and by extension the best firms, are those who proactively hire, support, and build up their future leaders. They expect their apprentices to become their masters someday, to be better than they were in every way. Akin to an extreme version of "A players hire A players while B players hire C players".