That is making the assumption one can’t get a great education at a school with a higher acceptance rate. Both my kids proved this wrong as they attended the best fit even though both were low on selectivity vs others they got into.
OP has bigger issues. Like all, budget is first, second and third most important.
I’m sure they get into UMASS - but is it too big ? Is a smaller - even UVM, UNH small better for them ? And how big are the math classes ? In that major, you’re not going to be with dummies. It’s like engineering - if they’re advancing through the program - U Maine or U Michigan, they’re smart.
Maybe an Honors opportunity at one trumps UMass without.
Obviously OP and their son will do what best, but I hope they choose against strangling themselves with such debt. Because that’s what it is - and then the job market isn’t a sure thing - and even tougher for certain groups which this student may belong. And obviously getting a funded PhD is a tough slog.
So I hope they find the right program in size, curriculum depth, and most importantly budget.
It’s hard to tell but I feel like this is a student who - to analogies, maybe runs around the backhand to hit a forehand - meaning maybe isn’t interested or desiring Gen Ed’s. That’s where a Rochester, Vassar, Brown and more may be better but obviously aren’t happening. But a Kalamazoo, which feeds PhD programs, has great merit and minimal Gen Ed requirements. We all know someone who has struggled with non major courses.
I don’t feel I have an exact handle yet on the student but to me, it sounds like smaller might be better in regards to the day to day situation - which the student will have to navigate no matter the school name. And less required classes might be better - ie the humanities side.