Yeah I wouldn't give up Borgstrom to move to #3. We can still get a great defense prospect at #15. Hughes is a brilliant offensive talent and probably the best skater in the draft, but there are still too many question marks around his defensive game for me, to consider him a slam dunk first pairing guy.
Even apart from the obvious guys, even Dobson, Bouchard, Smith, Wilde, and K'Andre Miller would all be top 10 picks in a normal class for defensemen. And others like Sandin, Merkley, Woo, and McIsaac would almost certainly be top 20. We literally can't mess up if we pick a defenseman. Even guys like Hughes and Merkley who if their defensive play never comes around should still be effective offensive weapons who should carve out nice careers in the nhl.