So regarding Matthews and the Hart... I think it's a fair knock on Matthews for games missed, though I think there are some huge flaws in some of the other reasons against him getting it. Namely that he's not the most valuable player to his team league wide.
For one, I see alot of people talking about Toronto being too good of a team for Matthews to have the same effect as someone like McDavid for Edmonton, or Shesterksin for NYR, but then there's this subjective qualifier that if you put up enough points above your competition you should get it even if you're on a great team. Seems like a contradiction.
I would also argue that the "good team" qualifier is also flawed. Just because a team is a playoff team without their best player does not minimize how valuable that player is to their team.
To put this in perspective, Matthews did something that's only been done twice in his lifetime with 60 goals (there was quite a few before that but its been rare the past 20 years,) and had a career year in both goals and points. He is strong defensively and on faceoffs, and is a league leader in other areas like takeaways.
It's not coincidence that Matthews' career year is also the year Toronto set franchise records for games won and points in a season. Who cares if Toronto might be a playoff team without Matthews; with him having a career year the team has literally had their best regular season of the modern era as well.
I think it's fair to argue that Matthews games missed negatively impacts his chances. I also think it's fair to argue some of the other great seasons by players around the league are more deserving, but I find the "not the most valuable player to his team" argument silly.