No, but so what? The guy behind 3Blue1Brown probably isn't one of the top mathematicians of his era. But he's having quite an impact. He turned explaining fairly basic math concepts in mathematics into a lucrative job.
And who wrote the textbooks you're referring to? Probably not any of the top 10 living mathematicians. That doesn't make the work less useful.
Is Linus Torvalds one of the top 10 computer scientists? He probably wouldn't describe himself that way, and respected academics mocked his work. The list goes on. I think this is compatible with the premise of the article: it's not about being best, it's about being better than the average bear - and then putting that knowledge to some productive use.