He had a bit of a down shooting % year. Production being down is nearly all PP related. NYI really had a difficult time with PP entries, made a lot worse with Barzal's injuries. When you look at even strength production, shots/attempts, possession stats, etc they're either in line for his career or else show improvement. The plan was a line of Duclair-Horvat-Barzal, but that really never happened because of Duclair's injuries (which imo he never really recovered from), and then Barzal's injury. The sh % was down for the same reason PP goals were down - fewer looks in the slot.
The eye test tells me he's had no physical dropoff at all. But like most 25-30 goal scorers, he's a bit streaky. I don't see that changing. But he can also do a bit of everything, including being a big bro who isn't a fighter, but can mix it up to protect his teammates. Not only is he fast, but while he's really more of a top end #2C, he can handle 20 minutes per night. He's that kind of athlete. I think he's gonna continue aging well. But he controls his destination.
