Even as a Leafs fan I will admit that MacKinnon is a better player -- at least right now -- than Matthews is. And I would admittedly take him over Matthews today if we had the chance.
For me, if we're removing all bias, this is simple -- MacKinnon is better than Matthews is every aspect except for scoring goals. He's a better skater, he's more explosive, plays with more intensity, produces more overall points, and he has shown that he can dominate for stretches in the playoffs. And, although Matthews "scores more goals", MacKinnon is no slouch either and has elite mitts. I also prefer MacKinnon's competitive spirit and fire than Matthews' nonchalant, ho-hum, play it cool, attitude.
All of that said, Matthews is still probably my favorite player in the league right now, and I'm thrilled that he's the cornerstone of the Leafs. But, yeah, full disclosure, I take MacKinnon over him.