> Humans have a tendency to ascribe intelligence to how well spoken a person or thing is

That’s true. I’m fluent in German, but there’s still a difference between me and a native speaker. I’ve often seen my ideas dismissed, only for the exact same point to be praised later when a native speaker expresses it more clearly.

I don't think that what you're experiencing is grammar related, I'd bet xenophobia.

Logos, Pathos, Ethos