Whiting can shoot. He and Trey were not similar players in high school and have not been in college. Whiting was a guy who was called on to score the ball from everywhere whereas Trey has never really had the primary role of putting the ball in the basket so far as I am aware.
I know you did not explicitly state they are similar ("It'd be like having another Trey..."), so maybe that is not your point. I am simply saying that they are not particularly comparable players.
Whiting is skilled. Like many excellent high school players, he may face challenges in terms of his size, length, and relative athleticism vs. enhanced size, speed and length. While Jace is athletic enough, elite defensive guards like those in the MWC and Big12 are problematic for most BYU guards, and Whiting would be no exception. Trey seems to compete well in terms of his quickness and explosiveness in the Big12, but his offensive skillset has been a limiting factor.
I would not write Whiting off as a potential contributor at BYU. I simply don't think he'll opt for the Cougs.