I have degrees from MIT and UC Berkeley. I can attest from experience that at such institutions, while there are indeed some professors who excel in both resea

I have degrees from MIT and UC Berkeley. I can attest from experience that at such institutions, while there are indeed some professors who excel in both research and teaching, the vast majority are there because of the quality of their research with teaching a secondary concern. Also, I think having a huge depth of knowledge is really not that important when teaching introductory topics (as long as you don't get anything wrong!). Having tutored students for many years, I'm quite certain that the biggest impediment to learning such topics is motivation, which is addressed more by a teacher's enthusiasm and speaking ability than the depth of their knowledge.