The reality is that a lot of different things contributed to the mess, to different degrees.
You had a large amount of turnover with key role players, and no the players they were replaced with were not necessarily better. Maybe if you looked at each in a vacuum you could make that argument, but having someone like lazar playing on the third line is not as good or better than a Zetterlund or Sharangovich.
You have a group of forwards who really can’t be relied on defensively, with two rookie defenders playing prominent roles trying to close that gap and also prop up veteran defenders who suck like Brendan Smith and a struggling Siegenthaler. The vets, including forwards, should be the ones propping up the kids not the other way around.
The goaltending sucked but it was really no surprise given what was in the front of them. A Swayman or Shesterkin would be the only guys who could mitigate the skaters deficiencies in any kind of meaningful way.
On top of that the team was filled with too many players who suck at winning board battles and are soft as f*** physically. Getting brutalized along the boards and with dirty plays because you have zero willingness to be dirty back leads to injuries and fatigue. And boy did we have plenty of that.
And then the base to all this was without a doubt the systems and coaching. There was just no way you were gonna survive all of the above without some outstanding coaching, but the reality is that the asinine system and lack of mature structure and accountability for playing responsibly greatly contributed to all of the above. I can’t imagine being a rookie defender trying to navigate this stupid defensive scheme for 20 minutes a night alongside Brendan f***ing Smith.
To further the point about coaching…this team looked like straight dog shit defensively for a good 15 games before the injuries even started. Even if they had a bit better fortune than losing Dougie and Jack for huge stretches, this team still would not have been anything more than a WC and would have been utterly embarrassed in the first round.