I note at 7406, Penn CAS alone had a higher undergraduate enrollment than all of Princeton, Harvard, Yale, or Duke. And you would further have to subtract from those totals their own engineering students, and anyone who was sort of Whartony.
Obviously YMMV, but to me this actually makes Penn CAS a great option for people into the sorts of things CAS does, but not so much the Whartony and Engineering stuff, and who want a somewhat larger community of like-minded students.