You’re right, going away and living in some random country for two years not playing basketball isn’t conducive to developing as a basketball player, especially right when they come home.
But when you get guys who have gone on missions, redshirt, then play for four years, I think there’s an obvious advantage there. Players coming home from missions are more mature. 23 year olds are stronger than 21 year olds, especially when they’ve been in a D1 athletic program for five years.
I don’t think missions make players better basketball players. But we all know there are mental benefits you can’t really get any other way. And those mental benefits can help in pressure situations like March Madness.