The Toronto Maple Leafs were the 10th overall team and had to over-achieve to get there. They were the 11th best team by expected goals percentage, and the 24th team by 5v5 save percentage.
The Toronto Maple Leafs finished first in 5v5 offense, and 19th in 5v5 defense. They literally lived up to their reputation as an offense-first bad defensive team, only this time they added a superficial amount of "snot" to their lineup to disguise it better. (stats from naturalstattrick.com).
They were underdogs against the Bruins, and took the series to a game-seven overtime coin-flip. Everyone is mad because of past losing, but by focusing on the past they are ignoring what actually happened.
Matthews, Marner and Nylander were sick/injured/not fully recovered from a previous injury. I doubt if one of them played a single game at 100% the entire series. John Tavares was used as a defensive player and Morgan Rielly was stapled to one of the NHL's worst puck handlers.
All of the things that happened are on the coach and the GM. Blaming the players if they don't perform is understandable, but the Leafs did perform. Despite some obviously less than ideal conditions they did better than the ideal version of their team was expected to do. Again, they were a 10th overall team that had to start on the road against (at least by standings points over a two year period) one of the best teams ever.
Being Out of the Playoffs Is on Management, Not the Players
Blame Kyle Dubas if you want - but he's gone.
Treliving had plenty of opportunity to re-make the team as he saw fit. Whatever you think of the job he did, you can't say he just inherited problems from the old regime. Those were Shanhan's problems and he co-signed onto them when he was hired to keep the core together. If he traded Nylander, he would have been able to blame the problems he has on Dubas, but instead he clearly just replaced Dubas as Shanahan's point man.
The new GM had $20 million to spend. He was left with 4 x future Hall of Famers and the option to trade one of them that didn't have a no-movement clause. He also had at least three prime assets to trade (1st round pick, Minten, Cowan).
So how did he do?
Here is the case against Brad Treliving.