> The idea of thinking independtly like that though seems unbearably slow to me

So, as a person who definitely has an inner monologue, I absolutely agree. It's not like I'm literally sounding out words in my mind all the time. The vast majority of things I do I do without explicit use of language.

I think my understanding (mostly coming from Chomsky and in disagreement when OP) is that language is a mechanism for thinking that is mostly not accessible through conscious introspection.