I took a Math 1A class (intro to calc) at Cal where the prof turned his back on class at the start of the hour, then proceeded to mumble incoherently for 60 minutes while filling a chalkboard with equations. He’d turn back around at the end of the hour. Many students brought pillows. I learned literally nothing in lecture.

This professor wasn’t demanding, he was just making zero effort to actually teach.

Great researchers are not necessarily great teachers, especially for intro courses. Anecdotally, I think this is a common issue at “prestigious” schools.