It was out of that judgement, that companies started to require degrees for office jobs of all sorts, as you could discriminate based on education but couldn't on an arbitrary IQ test. And naturally, tests on the topic of a job can also be administered.

And I do think you're right - Leetcode does select for recent graduates who likely were taught in a throwaway language for academic purposes. And selecting for young college graduates are highly likely what they're searching for, as they also do not know their worth.