I asked my D, a PhD student at a state flagship univ., and she told me that it was not necessarily correct. This is what she said, “Compare the class I taught last summer, with about 300 students, 10 TAs, and 20 readers, with XXX class taught by Dr. YYY this semester, with 1500 students, 55 TAs, and hundreds of readers. Dr. YYY is so busy managing the army of TAs and readers that he doesn’t even have time for office hours. When I was teaching, every office session (twice a week, each 1.5 hours), I had 15 - 20 students needing to talk to me, and I had time for them. I don’t think Dr. YYY has time for 100 students each session.”
There are definitely some good TAs, but noone knows the materials as profoundly as the instructor, who is responsible for developing the materials.