The downside to Lee isn't projecting his shooting percentage, which doesn't even factor in his ability to cause goals he doesn't touch. He assisted (in the non-technical sense) on many goals this year by blocking the goalie's view. His shooting ability in-close is sublime. There's no luck involved. Having the strength and hands to hit the top of the net in close is a sure-fire way to score. It's just incredibly rare for a player to have those abilities.
Still, Lee's downside is his defensive play. He is not quick enough to help down low defensively, and come back high for break-outs. And even when he sticks up high, he tends to get beaten by pinching defenders. It just takes him a long time to get going, and he doesn't have the defensive hockey sense to make up for his poor acceleration. IMO if Lee was better at getting NYI out of the zone, that line would've scored even more goals, and let up far fewer. As it was, only Josh Bailey was proficient starting breakouts from the wing.
He is better off as a sheltered ES player who is featured on the PP. That's what hurts his value IMO. Otoh, he's a great guy and totally committed. He'll keep himself in peak physical condition, and should have a long career.