You're making some big assumptions. At my university, every Ph.D. candidate must take comprehensive exams. Depending on the department (and faculty) they're administered differently. In engineering (where I did my Ph.D.), you had to do a proposal which was submitted to your committee. Then, you had an oral exam. Half of which was questions on your proposal and the other was about your background knowledge in the field. It could take as long as they wanted. Mine only ended because they wanted lunch (it was 3.5 hours long). Also, you were required to take 3 courses, which you were pretty much expected to complete before your comprehensive exam.
The 3 papers makes a thesis also ignores the fact that it needs to be a coherent whole and pass the thesis defence, where the committee includes both a person external to the department and one external to the university. While I'll grant 3 papers is probably a thesis, it entirely depends on the papers.
Everybody in STEM courses at my university did both an RA and a TA unless they had a large scholarship and didn't need any extra money. In the CS department, it was actually expected (I was co-supervised by a CS prof for my Master's so I know what the other people in my lab did).
I had a girlfriend who did her PhD in Mechanical Engineering and she was actually required to do contract work in her lab. She couldn't even get paid for it and was still required to do it. She was in the Canadian military and they were paying for her to do the doctorate so she couldn't get paid from anyone else (but she had a scholarship which was allowed). The contract work delayed her thesis research, but the professor required her to do the work. So, you're extrapolating your knowledge and assuming it's the same everywhere which isn't true.