That's rarely the case in most universities. The instructor may have a very good understanding of the subject material but no idea as to how to convey it. Many of my instructors could barely speak english. You learn from the textbooks or you fail.
This is VERY different between institutions and levels of institution and majors. I went to a top 20 national university. I had one adjunct professor in 4 years (an English PhD student who taught a small 10-person freshman seminar).
I never had a teacher who was hard to understand. My Calc 3 teacher was German, but that was it. Every single computer science professor I had was native American or 100% fluent and clear in English.
My freshman 101 comp sci class had maybe 60 people, and that was the largest class I ever took. Multiple undergrad professors held parties at their homes at the end of the semester for their students. 20+ years later I am still in regular contact with 3 or 4 professors.
My experience in graduate school was identical. My wife went to a small private liberals arts school and her experience was perhaps even more extreme than mine. She never even had a 60 person class!
This all came with a price tag that has gotten worse since then, of course..
My sister, on the other hand, went to a non-flagship public and her experience was wildly different. I'm not sure she really ever had personal interaction with a professor. It was very much what you said--learn from the textbooks, pass the exam, that's it.
