look, it's not perfect. A returned missionary in most instances is significantly more mature than an 18 yo simply because the RM has had more life experiences than most 20 year-olds that haven't served a mission.

We have two on-campus instances among our sons.
First son came home late enough to miss the fall semester. He already had one year in Helaman pre-mission. He was interested in getting married when he got home, but he left us with little to no instructions on getting set up post-mission. We simply called Heritage and got him in. Unfortunately, he was one of half a dozen RMs in the ward. His dating scene was pretty limited, but it was only one semester.
Second son, also stayed in Helaman pre-mission, made arrangements with his HS best friend and found a place off campus...easy peesy. FWIW his HS best friend had already been home for a year.
Third son: He wanted to room with his buddy from HS - incidentally the brother of roommate of our second son. So, the moms worked on finding housing. They had several leads for off campus housing and they all fell through. So, they got them in an older heritage ward. Both of these boys will be freshman and while we all thought off-campus would be better, it's just one year. We also felt as a first-year student, Heritage would be a better way to integrate them into school.