My advisor strongly encouraged me to check out two (highly renowned) American universities for my PhD study.
Her collaborators in these two institutions are good people and great mathematicians, so, assuming I can get in, working there would be very pleasant.
However, I'm confused by the structure of these graduate schools. In the first two years I'm supposed to follow courses and do a comprehensive written exam and an oral one which are mostly about topics (complex analysis, basic functional analysis, ODEs) that we do in the first two years of undergraduate study in my current institution.
The exam questions from the past years appear to be quite difficult, but revising those relatively elementary topics and spending a great amount of time solving difficult problems on them seems like taking a step back after a Bachelor's and a Master's degree (which had a quite significant research component).
So my questions are the following:
what is the rationale behind this structure of graduate school in the US?
why is it effective?
should I be concerned about "wasting time" revising basic topics in my area instead of diving directly into a research program after a Master's degree?
Added context from comments:
"Students who already know the material can take the exams in the first month of their Ph.D. program" is exactly what my advisor's collaborators told me. However, although the core material is well-known to me, it appears that the exam consists of many problems in a short amount of time and that such problems are mostly about clever ways to sum series, evaluate multiple integrals, do contour integration, solve tricky ODEs, and so on. That is, it is about elementary things but requires lots of exercise. That's why I'm concerned that it could be an unnecessary detour.