The same way some people wanted to trade Benintendi a few weeks ago for peanuts, young guys need time, some become all-stars out of the gate, some need some seasoning.
I disagree with you on Chavis, he might not have the talent to stick around for long, even in that case, you stick with him he might surprise a lot of people, including me.
Devers and Benintendi are the real deal, by the way, it's unfair to place sky high expectations on them, the league will adjust and they will hit some rough patches, but it's not a good reason to give up on them.