I mean, he doesn't play centre. I don't know if he ever has, at best it was a decade ago when he was still in the GTHL. You can move around LW-RW, or a C out to either wing, but if you don't play centre, you don't play centre, you're not picking it up at an NHL level a decade late. It's just not transferable, there's so much more going on then wing, they are radically different positions.
Nylander, who did play C all the way through until he hit the NHL, is too far behind the curve now to crack NHL centre, there's proof of concept for it. Marner couldn't possibly.
No point ligating the second part, there's probably literally tens of thousands of posts on it.