>mediocre people will produce even worse work and will weed themselves out.
[[Citation needed]]
I don't believe anyone who has experienced working with other people - in the workspace, in school, whatever - believes that people get weeded out for mediocre output.
You can also be mediocre in a lot of different ways. Some people are mediocre thinkers, but fantastic hype men. Some people are fantastic at thinking, but suck at playing the political games you have to play in an office. Personally I find that I need some of all of those aspects to have success in a project, the amount varies by the work and external collaborators.
Intelligence isn't just one measure you can have less or more of. I thought we figured this out 20 years ago.
Weeded out to where anyway? Doing some silly thing, like being a cashier or taxi driver?