Nylander is a star hockey player having a career year. If we pay him 11m, we will regret it.
Marner is less of a hockey player and moreso the physical manifestation of a swirling mess of narratives. He's the golden boy, the local kid who was the chosen one, who seems to be eternally tormented by the slings and arrows of outrageous fortune. Doug Gilmour, flipping pucks over the glass, hockey dad from hell fighting people on twitter, this guy is anything but a normal hockey player. The actual human being Mitch Marner has absolutely sick talent, but mentally he's got to be the weirdest hockey player I've ever seen. Wound up tighter than (insert favourite tasteless metaphor here) and prone to implosions when we need a hockey player to lead us.
Marner is more talented than Nylander, there's no real doubt to me about it. But I don't think Marner can win in Toronto, he's got too much going against him mentally. If you love him, let him go somewhere else where he can be free.
That's what I'd do. What the Leafs are going to do is let Nylander walk as a UFA this summer and re-up Marner next summer to a 12m contract that comes with the captaincy.