I feel weird defending Sidney Crosby but as good a season as both those players are having, the Penguins were sellers at the deadline and had basically thrown the towel in on the season. Malkin has looked like a shadow of himself at his peak, Letang is wildly inconsistent, and goaltending has been spotty to bad. There are big holes on all the lines and the D is a mess. If you view the Hart as the MVP of a team, and some do view it that way, the Penguins would be an AHL team without Crosby. The Lightning and Avs would still be very good teams without Kucherov and MacKinnon.
Granted, though, he won't win, even if the Pens find themselves in the playoffs entirely due to Crosby's efforts. But in my mind there's no one player in the league more valuable to his team.