I disagree that the Sabres rushed him. If you're looking at his stats, including age and size, sure, probably looks risky.
If you watch him play on a nightly basis, you know he's an effective player in all areas of the ice and is very steady emotionally. For example, they're using him on the pk now because although you'd normally not want to put that on a rookie, it's clear at this point he can handle it and he likely will improve the pk!
He goes to all the dirty areas and regularly comes out with the puck against guys who have 75 pounds on him.
There is zero reason to send him back to junior hockey, IMO. He's just going to get better developing at the nhl level.