I thought there is one point you didn’t mention: good researchers are not necessarily good teachers. At Brown I’m assuming people got tenure by being at good research, and teaching is simply part of their departmental responsibility that takes time away from research. And so some researchers treat teaching like a chore, with added contempt to boot. Yes, as you mentioned, the top 1% will thrive despite the best effort to sabotage their learning experience, but there really is no point in humiliating the 99%.
I’m sorry about your experience as an undergrad, it is particularly appalling. I have a maths degree, but originally I was majoring physics. My physics degree in my university (University of Auckland) is structured so that I did enough maths papers to qualify for a math degree, so I did. Maths is more about logic, but physics is more about modelling reality, with maths. I remember one physics lecturer specifically said he will teach us just enough maths so we can do physics, but no more.
So my guess is, your particular experience is because of the hubris of your particular teacher.