The universities are filled with immigrant professors with accents so thick that you can barely make out one sentence. They couldn't teach well enough to save their daughter's life, but they're really good at passing exams.
I don't recall having a single immigrant professor at any of my schools except one Hungarian refugee who was a right wing fanatic, and I liked him.
The ability to teach, imo is more inborn than learned. Sort of like being a sprinter. You can improve a little but you can't put in what God left out.