He wants to develop his game and play against the best competition. If he likes BYU and all it stands for, the coaches and system etc. Going to CA for one year isn't going to necessarily change that. It will come down to what he wants and the college program he thinks is best for him, as it would if he stayed in Utah.
With BYU on the rise and making the NCAA tournament, which I expect to continue, I do not think BYU is at a disadvantage to many other programs out there.