> "managers" have been the least important part of any team, and had the least impact on success or failure

I'd disagree...I think it can be difficult to see what the manager brings in when a team is good and runs well enough. It's a lot more obvious when you get a bad manager: the team stagnates, loses focus, valuable members will quit (there's the saying "employees don't quit their jobs, they quit their bosses"), recruiting also becomes harder.

There's too much to discuss in one comment, but managers that don't seem to be doing much while the team members are killing it are a precious breed and worth their weight in gold. An alternative way to look at it: they don't need to brag about being important, and have at least enough grasp of what their team does to not be standing in the way.