As to the first part, Just watch his shifts when the opposition has the puck.
Watch his eyes never leave the puck. Watch him skate in a circle chasing it around, mesmerized by it, never checking for other open players that he would be bettered served to cover, never looking up to evaluate the big picture on the ice.
I think in Junior, his puck hounding tenacity does serve him well to some extent, with his athleticism allowing him to likely disrupt offensive execution before the slower reacting players can make plays, but it tends to lead to bad habits and poor on-ice awareness.
The second part i completely agree with. I don't watch OHL hockey, so I don't know if he plays differently than when he is playing in the AHL, and it may all just be nerves and him panicking as to why he dishes the puck as soon as he gets it, but I would think he wouldn't have nerves in juniors, and I think you have mentioned that he did the same thing with Kingston usually. That could be just not knowing any better, but it all comes down to an inability to read the situation and take advantage of all options, and I would think learning that as a 19 year old in the OHL will be easier than in a higher pressured situation in the AHL - maybe a small silver lining if he is not eligible for Coachella.