Every player makes mistakes every game. That's not at all the issue with Nylander. With Marner I never have to question his work ethic, his desire to win or his commitment to the team, because it is all very obvious from his play. Marner is a heart and soul player through and through. And yeah, he f***s up sometimes, but you live with it because you know 100% he gave it his best effort. Marner and Nylander are approximately equal in talent but Marner is the far superior player because of his work ethic and heart.
You also have to consider how having a lazy yet talented player effects the team morale. You have guys on the third line working their asses off every shift and then Nylander is just out there coasting half the time. That must rub guys the wrong way.