I would agree that there are competent developers who want to stick with a single thing and aren't interested in changing languages. The distinction for me is

I would agree that there are competent developers who want to stick with a single thing and aren't interested in changing languages. The distinction for me is that competent is not necessarily good. For me, good is a higher bar than competent. That's why I said any good developer, any one I'd want to work with (as you say), wouldn't be a problem with switching languages.