In your opinion and thats fair but in my opinion I'd take the 21 year old top 4 d trending towards a top pairing d man. Winger is the easiest hole on a team to fill, top pair d not so much.
He is 22, btw. I think there are legit reasons to question Sandin's ceiling because of his physical tools, but he would certainly be a nice piece in a proposal. If you really think he is a future top pair D, though, it seems questionable to use him for a rental. Makes me wonder if you really think that's what he is going to be.