I’m not sure you can make a big school small or a small school big. The advantage of a big school is, with more people, you may have more groups to explore. The advantage of a smaller school is if it is a good fit, the whole school can feel like a second home.
Perhaps it is somehow influenced by admissions, but William & Mary has the highest alumni giving rate of all national public universities, ranks tops in Princeton Review for “Happiest Students”, and has one of the highest four year graduation rates for public universities.
If he can visit both, he’ll probably get a good sense for fit because they are quite different in size and location.