You don't shelve a potentially generational talent in minor leagues for two MORE seasons just because you can wait that long to have to add Chourio to the 40 man roster - my goodness. We're not talking about a 30th round draft pick out of college with a fun nickname or Cooper Hummel here...
If he stumbles in his development, sure, you have the luxury to let him struggle and grow as a kid in the minor leagues - when he's doing what he currently is at the AA level as a teenager, which is frankly making a mockery of it during this recent hot streak, you start figuring out how soon his talent can help at the MLB level and get aggressive in getting him up there.
A full season of Frelick, Mitchell, and Wiemer should never ever be guaranteed due to the injury histories and some initial MLB struggles - and frankly even a healthy full season with those 3 in the outfield wouldn't be as good as having Chourio on the MLB roster as an everyday player - even as a 20/21 yr old. He's that talented.