BYU, with the same players, not serving missions, is a far better team.
Missions are a big net disadvantage to BYU's athletic program. Without question. I tire of even BYU fans trying to concede on this at any level.
The ONLY reason BYU might benefit is because they might be getting better athletes who want to serve a mission but would have gone elsewhere if other schools would have allowed them to go.
Some individuals do gain advantage by serving a mission, but the number of people that are hurt (athletically) by a mission far outweigh those that gain advantage. If you served a mission and played college sports (and are not trying to assume the role of encouraging HS athletes to go on missions), you know this to be true.
Saying that a specific player is better because he's older, more mature etc. may be true, but that is only for that player. The program itself suffers tremendously in lost talent overall.
If missions were an advantage, other schools would not only encourage LDS kids to go on missions, but they' send the other kids off to the Peace Corps with a wieghtlifting and diet program to follow.