I don't know. I think the big problem is, it's just way too hard to tell in the regular season. He still cuts to the middle of the ice for most of his plays and hangs on to the puck for quite a while to dish off a great pass. And...it's kind of a work of art. He's truly one of the best at those things. It is honestly incredibly impressive.
But in the playoffs, cutting to the middle of the ice doesn't work as much. The opposing team clogs the neutral zone, shrinks the space, and initiates contact at hight speed. Unless you can make space for yourself and bulldoze your way through, players like Marner are pushed to the perimeter. Even from the perimeter time and space is taken away, and unless Marner is no longer afraid of that contact...he can't hang on to the puck as long for that perfect pass and ends up almost throwing it away leading to give away after give away.
He's playing great, but how can we tell based on this play that it will be different when the style of play he's up against changes?