What I've read (and watched) suggests exactly the opposite. College has too much freedom compared to high school, so most of the time bonds with classmates seem much smaller, since they don't stay together as long, unless they're tied by other elements, like shared interests. That ends up favoring high school since it's a more universal and tightly knit experience.
On the other hand, if anything, actual high school in Japan has much less freedom than portrayed in anime since studying for university entrance exams is a big focus in reality, while most series sideline that, or portray it in a way where it doesn't take time from random clubs or hanging out with their friends even during the third year.