I cannot say I've watched either player live that many times, so I can give credit on that.
When you say "Big", one player is 5.11, 165lbs, the other is 6.02, 180lbs. There's a size difference. Both can score goals, Fitzgerald might be better is this particular department, shot for shot. Finesse for finesse, I'll do with Di Iorio in the goal department.
Fitz is also much more physical, which translates a lot better at the next level, OHL, even to pro on a wider scale.
I will gracefully disagree with your other points, Di Iorio is a better skater with better acceleration and top speed while being able to do more with the puck in a skill and passing capacity. Di Iorio can also play in all situations, while knowing what to do in each at a higher level -- making him an overall better 200ft player & IQ. I dislike comparing scoring from league to league because of over strength of league -- I don't discredit the overall numbers, but there's "levels to this sxht".
Also, non taken on the response, I like to banter when it comes to hockey and players' abilities, nothing is ever personal