After Kobe averaged 7.8 points his rookie season and was bricking shots in the playoffs, did you KNOW he was going to be in the discussion for GOAT? Don't be disingenuous with your response. After 2 years, did you know Stockton was going to be one of the greatest PG's ever (he wasn't even a STARTER!) and it wasn't until his fourth season he averaged >8 pts/per. Anthony Davis certainly had a nice season his rookie year (14/8), but he wouldn't have won this "homer" game. Or how about Kawhi. Yes, I realize you knew without a shadow of a doubt after his AMAZING rookie season of 8 pts and 5 rebounds that he would be the Finals MVP just two years later. All players definitely come into the league at the same levels of development and you can project with 100% certainty their career trajectories.
As for Vonleh, if he goes to any other team besides Utah, he'll get a ton of minutes and will likely average a double/double. If we can say A. Davis justified his #1 draft position at 14/8, I'd say 12/8 range would be good enough for a #5 pick. Or was Davis a rookie "underachiever" who exploded into one of the best in the NBA in year 2?
If Vonleh lands in Utah, he may only play 20 mins/per. And the same would be true of Randle. Kanter and Favors are the starters and Gobert will get some time in the rotation as well. So barring injuries, less minutes available for another big in Utah than elsewhere.