Whoa ^ …that is a very bold statement to make, if it is true.
Here’s been our experience for the past 3 years at UA.
In those large ‘introductory’ STEM classes (think level 100s and maybe the odd 200 level), there is often a lecture taught by the professor…and then there is often a recitation (or a lab) which may be taught (more like overseen) by a graduate TA. My son’s Statics (200 level) class was actually taught by a PhD ‘student’, who had finished her PhD, but I don’t believe she was fully hired as a professor, but was certainly qualified to be a professor and was more than capable of teaching that class. My son was asked to be a TA once for a freshman-level class, but his role was going to be (as I understand it) more to circulate and help - the professor was still in the room at all times. He declined, so I don’t know actually what he would have been doing.
In the smaller ‘major’ classes (as in classes required for your major), all have been taught by a professor, too. In son’s non-STEM classes, he has had nothing but professors, except I believe in Chinese there may have been a graduate student at one point (who was from China, so perfectly capable). In any Honors class, regardless of the subject, it will be taught by a professor, full stop and this has been our experience with all honors classes he took: definitely no TAs there.
So, perhaps it is true at UA that only professors teach all classes? I didn’t think so, but reflecting back on son’s 3 years, that’s pretty much been the case.