Actually, it seems to me that your son's results were pretty good. He got into a highly selective college in a tough year, and into three other places that are more affordable.
Only a tiny fraction of kids are getting into most of the top-ranked schools they are applying to. Admissions can be very arbitrary. You don't know what the colleges are looking for and how they are trying to balance a class. It's frustrating to see kids who are no more capable than yours getting into places at which your S is rejected. But you also don't really know the whole story, the whole record, of these other kids. So it's a waste of time to compare and stew.
You should certainly not feel guilty. Your son has 4 choices. That is good. Too many choices can be a burden also.