FWIW, I was the dumbest person ever to graduate with a physics major at Cornell, and even I as a senior was taking courses co-listed with the graduate school.
I’m sure I could have taken more advanced courses if i was up to it.
Back then the “good” students were somehow identified, siphoned off, given great research experience, and went to top PhD programs. I don’t know what the process was, but it happened. Whereas I, being the dumbest person ever to graduate with a physics major, didn’t. Which was fine with me, it would have been a waste of time for all involved. But that was a long time ago, and undergrad research has become a much bigger deal these days. I’ve no idea what they do now, you should ask them. But it must happen.
Between Physics and Astronomy in CAS, Applied and Engineering Physics in COE, and other areas in COE, (eg Material Science) the amount of advanced level courses available there, including graduate level courses, for a physics major is staggering.
Cornell has a much larger student body though, true. And it’s very diverse, in terms of student types and interests. Only 30% of the students attend CAS. And lower level class sizes there are not small.
If a smaller environment is the overriding preference, I personally would choose Dartmouth. Unless I knew for sure, eg based on multiple visits and an overnight, that I fit in really well with the prevailing campus culture at Williams.
If the Physics thing isn’t happening, I can see a science-math oriented guy sliding over into engineering science. Engineering in some capacity is actually a pretty common destination for physics grads. Or computer science, which they both offer but at which Dartmouth is actually somewhat reputable IIRC. And the fact that it has three times the enrollment might make it slightly less boring.
As I mentioned, my reservations about small school in small town derive from my D1s experience in same. Though not at Williams.