As an Islander's fan, I'd be very interested in getting Nylander. I think he'd be a perfect #2 center behind Barzal. So it's an interesting proposal.
I think the Isles love Dobson, he literally was a gift from the hockey gods, the Isles have nobody of his skillset. Don't let the draft slot fool you, if you watched the draft, several experts had him top 10, some rated him as the 2nd best Dman in the draft. So just like stats aren't always the be all end all that sums up what the player is. The draft slotting isn't always a factor. Example: 2008 Draft, Erik Karlsson was drafted 15th overall, yet is the 2nd highest scorer in the entire 2008 draft, and the best dman from that draft. 6 defensemen drafted before Karlsson. So don't let where Dobson was drafted fool you. History shows that it doesn't always wind up the way the draft was slotted. Not saying Dobson becomes as great as Karlsson, just making the point about draft slotting can be overrated.
Me personally, I'd have a hard time trading Dobson straight up for Nylander, The projection of what he could possibly become, is too high to give up. Quite possibly another Alex Pietrangelo. A right handed, 1st pairing dman with good size, and excellent all around play, is extremely hard to give up. I don't think Islander's management would do it either. I think they know what he projects to be.
Now Bellows, I'd be more agreeable to give up. Though I love him as a prospect, and feel he will be a 30+ goal scorer in the NHL, With Oliver Wahlstrom being drafted, it wouldn't hurt as much as losing Dobson. I'd do Bellows and Dman Bode Wilde, who has a ton of all around talent as well. Great skater, excellent size, offensive mindset. That seems more fair.