Great teams beat great teams and great players have to beat great players... and going into those series we got our fair share of hype about how Toronto was the superior team with the superior players.
We were not the superior team in all of those series, before even factoring in injuries/suspensions, and we're not talking about overall team quality anyway; we're talking about ability to limit an individual's production. How Columbus is offensively really has no relevance to that, but the fact that they were the best defensive team in the league that year, despite missing their #1D for a significant portion, is very relevant.
Marner has faced an extremely unique situation over the past few years, where his only playoff games have consisted of everything that can make production harder happening at once. The funny thing is, Marner has actually largely overcome those factors and outperformed the skaters he has faced to generate opportunities, but goaltending has such a massive individual influence on the game. I'm not sure why there's such a refusal to acknowledge the level of goaltending we've faced over the past few years, when it's, quite frankly, obvious and undeniable.
It's fair to want to see more, but it's important to actually understand what's happening, and why. There is a lot that factors into playoff point production. You can't just compare across teams in the same way as regular season points, while ignoring the differences in what they've experienced.
This lack of uniqueness to what the Leafs have faced in the playoffs is especially obvious when you look at guys like Point, Barzal and Aho, whose teams have played and beaten teams like Boston, Columbus and Montreal in the same Eastern Conference playoff milieu over the past 2-3 years.
Not sure why you mentioned Barzal. He didn't play any of the same teams in the same years, and his playoff resume in general is nothing special. The only same team Aho played was 2018-2019 Boston, and he put up 3 points in 4 games. Again, nothing special about that or his playoff resume.
Point has done a bit better, though how much of that is because of him and how much of that is because of Kucherov is very much up for question. He finished strong against 2019-2020 Columbus when their goaltending collapsed, but he also had just 3 assists in 5 games against Montreal this year (even though Price's play had dropped off quite a bit by then), so it's not like he's immune either.
Connor? 3 points in 4 games.
Pacioretty? 3 points in 6 games.
Ehlers? 1 point in 4 games.
Dubois? 1 point in 4 games.
Stamkos? 1 point in 5 games.
Wheeler? 0 points in 4 games.
Scheifele? 0 points in 1 game.
Stone? 0 points in 6 games.
It's not like Marner was alone in this impact.
In terms of criticism and what you feel is right, this ultimately boils down to is how invested an individual fan is in an individual player.
Insulting players and making false statements about them is never right. Has nothing to do with "investment" in the player.