Marner has disappointed no doubt but it seems strange that he is the focus and not Matthews.
Matthews was horrible too, but Marner has largely underperformed in the playoffs in the worst fashion for years now. Most of his points have been power play and even this year he had half his points come in the first two games of the Tampa series. Not only does he not score, but he also actively hurts the team with noticeable turnovers and Jake Gardiner level plays under pressure like the infamous puck over the glass.
There are more moments of him directly costing the team and choking than any of the other big 4 or Rielly. He didn't even score a single goal against Columbus or Montreal.
He also poisoned the well with milking every last cent out of the team in contract negotiations.