If you have a team of quality people but they're all running around in their own direction doing their uncoordinated thing, they add up to basically zero. While if they're all working towards the same thing in the same direction, their efforts reinforce each other so the whole is much greater than the sum of its parts.
The expertise of people on a team provides a ceiling for what they can accomplish, that's true. And so you need to make sure that if you've got a task to achieve by a certain date, that it's below their ceiling. The best manager can't raise that ceiling.
But you still absolutely need to manage them in order for them to get anywhere even close to that ceiling. And to go back to your sports metaphor, when an amazing coach replaces a terrible one on a sports team, it's astonishing the difference it makes -- you almost can't believe it's the same team. It's astonishing what happens when a sports team plays "as one" instead of each player doing their own thing no matter how great they are. But that simply doesn't happen organically. It requires a coach, the same as a great team of employees doesn't get there without a great manager.
So ultimately it's not that either matters more than the other. You need both individual expertise and management. Think of the total resulting effectiveness as a multiplication of those two values.