The whole bunch of them have been awful and Marner being the scapegoat will turn into a Larry Murphy situation if he is moved to a team with structure and leadership. Book it.
As much as people love to toss out the Larry Murphy situation, he was in over his head in Toronto. They wanted him to be the everything defender, which he was not. It was the best move for Murphy and the Leafs. We can debate the horrible return, but it was the correct move. Murphy was getting eaten alive in Toronto. Coach Murphy didn't do him any favors, by how he utilized him.
It very well would likely be similar to that move, but we've already had one of those, when 2 time Cup Champion Kessel was dumped. Which was a great move for Kessel. Better Leafs' drafting could have evened out that trade.
However, marner is unlikely to be traded unless he refuses to sign an extension and choses a destination he'd prefer.