@yeetskeet1 You really overlooked some excellent math depts at flagships: UMD, Penn State, UMN-Twin Cities, UWisconsin, UWash. Also, UCSD . Math is usually not an impacted major at these universities, and since they all have excellent PhD programs, you won’t run out of courses to take as an undergrad. As someone with a PhD from one of the universities listed above, I can attest that their undergrad programs in math and physics are quite challenging.
At any rate, the college counselors at your boarding school should be able to help you sort this out much better than we can. For example, they can possibly suggest which one to do an ED at. My bet would be a Cornell ED app. HYPSM look for much for than what you have to consider for ED/SCEA etc.