Quoting: ChiHawk
I don't think Marner is better then Kane hands down; that's a falsehood even if taking defense into account. Look at Marner's stats away from Matthews or JT, both worldclass centers, and while still decent are Kane level. Kane on the other hand plays with a constantly revolving door of average centers and often not top end wingers. Contrary to popular belief, Kane doesn't play with Toews that much, and has spent more time away from Cat on the other wing then with Cat on the other wing. Then consider the two teams as a whole and who over the last few years is much better...that matters as well.
You can make an argument last season Marner was better i get that, but outside of last season no way. Kane slumped for the last 20 games last season, it's not excuse and it's real and needs to be taken into account, just like Marner is in a slump not...not an excuse and it's real and needs to be taken into account.
It's certainly debatable, and considering what Marner looks like to start this season, it makes it easier to take the Kane side of the debate.
The Athletic just came out with their Top 100 "tiers" ranking.
They had Marner near the top of the 2A franchise player ranking, considering TOI playmaking, defence, PK ability "Marner is an elite playmaker with solid two-way play".
Kane was middle of 3A all-star player tier - playmaking and offence among best in the league, but he gets knocked down for his defence "but his defensive limitations do hamper his overall play. The Hawks allowed three expected and actual goals against per 60, something Kane’s offense wasn’t able to cover up."
End of the day, Leafs trading Marner for Kane wouldn't make sense based on the age difference alone.