You mean Wagner isn't a better player right now than Garza even though he might be more talented?
Talent has to do with a combo of skillset, physical attributes and NBA upside. There's definitely a projection element involved with it. If NBA scouts think that in 5 years, Wagner better fits the mold of a prototypical NBA small forward and can defend that position at a high level, he'll be drafted higher than someone like Garza who projects more as a backup 5 in the NBA.
But lets be clear, the top 5 incoming HS recruits have a track record of being All-American type players generally during their one year in college.
There's always a few experienced guys who've been around in college for a while and bloomed late who are on the same level like Malcolm Brogdon, Josh Hart, Brice Johnson, Denzel Valentine, Luka Garza, etc. etc.