I don't think a warm up is a requirement as a part of every class, personally. Beginning basic group classes, yeah. ok. But at a certain point, some classes are attended by more experienced people and we are expected to know how to warm up beforehand on our own before class. I would get annoyed with wasting precious instructor knowledge time on a basic warm up that I should know how to do myself. I attended a stretching class as a beginner. They did two person stretches. I had some young person who did NOT understand older people tend to not be as flexible. It took many years before I attended a stretching class again. To be fair, I think that instructor was not the norm. I have since been near stretching classes over the last 16+ years and have not seen two person stretches. So maybe our Sifu stepped in and put a stop to that when he heard?? The stretching class I did go to until COVID did not have two person stretches and was run by an instructor I hold in extra high regard. She got me past my reluctance based on my initial experience. Covid aside, I would only trust a very few of my closer fellow students to help with my stretching. People I trust to go slow and listen to me.