Just looking at stats, Silayev is 207 pounds (looking at the elite prospects page). Kid needs a good 25 pounds, at least, if he wants to survive as a physical player in the NHL. I haven't seen the kid so I have no idea if he can put on that weight, or be like a Logan Brown and stay a string bean and get injured all the time.
That is one of the things you have to look at with the really tall kids. Height is great, but you also need to be able to put on the muscle to protect it, too. Especially for a defenseman.
But like I said, I haven't watched this kid at all, so I have no idea.