Grass is greener syndrome.
I've read a lot of posters say something along the lines of "at least those guys played with heart, were a hard working team, etc".
Being the only team to not win a playoff round in x amount of years was FAR better than being the only team to not make the playoffs for the most years.
Dubas made some mistakes, but the majority of those came from his first year or two. Signing JT was a risk that didn't work out, but that's a very unique situation and its tough to pass on a PPG centre wanting to come to Toronto.
The Marner contract shouldve been avoided by agreeing to a deal the year before (8x8 was rumoured to be offered by Marner at the time)... He hadnt fully proved himself yet, but everybody knew the following year would very likely increase his demands. Like it or not, Matthews will likely set a new market high each time he signs a new contract (same as McDavid, Mackinnon, and other top 5 players).
Other than that, there's some questionable moves but fairly few egregious ones (no Foligno trade/Mrazek contract are not egregious... there's been far far worse across the league).
Dubas of today is significantly improved over Dubas from 3 years ago and he shows a willingness to alter his plans as necessary. I think Shannahan was right to have some pull over big decisions in the past, but wrong to not allow for Dubas to have more autonomy now.
I'll support Trev/whoever our new GM is, but there isn't a lot of quality candidates and there's a good chance we're downgrading.