in theory he's worth at least a late 1st ...you typically do not expect a late 1st to be a 15-20 goal scorer, and the probability of a late 1st making the nhl as a top 6 player is low, and about 50% to even make the NHL.
Robertson has an elite shot, and just scored 15 in 69 games playing in the bottom 6, if the Leafs were a weaker team and had him in the top 6 and gave him 15+ mins a night, and some PP1 time, he is an easy 20 goal guy.
you can hope for that production from a late pick, after 2-4 years of development, so, a late 1st is actually a good deal for Robertson for whatever team was lucky enough to get him.
anyone that pays less is getting a steal, and GM's should be all over this guy for his untapped offensive potential.
defensively, he is a hustler and decent on takeaways, and wins more battles than he loses which is good considering his small stature, but, he is small, and can get manhandled on occasion.