I 100% agree it's time for Shanahan to hit the bricks. He was only hired because of who he was as a player, he had no real experience in an NHL club to warrant running hockey operations. If you want to hire him in a ceremonial role and have him do PR, fine.
I would say I liked, but didn't love Dubas. I'd give him a B. Pretty good but nowhere near great. I understand the Tavares signing at the time it was done. Here was a top UFA that was willing to come to Toronto and was not over the hill. Dubas' biggest mistake by far was the Kadri trade. Not because he traded Kadri, but because of what he got in return. Kerfoot never really panned out as a center, and it was never going to work for Barrie. He was not what the Leafs needed at the time. The Tavares signing ended up hurting the Leafs big time in retrospect for sure but you can't force them to sign a contract.
Dubas did some good moves like getting Campbell and Muzzin. I think taking a bet on Murray was a good move given they got him for literally nothing and didn't commit to the 5x5 Edmonton ended up giving Campbell. Murray was a bust but he's gone at the end of the year. Samsonov had a good year and although he fell off this season, it's not like he's signed long term.
As for the contract extensions, I think there's only so much GMs can do even with RFA. Yes, you can always hold out and make them sweat but then you're risking pissing them off and losing them. So all in all, Dubas was OK. When Shanahan announced the he wasn't giving Dubas a new contract, I wasn't opposed. It made sense, Dubas' tenure had been marked by failure and he wasn't able to get the team past the hump. He gave up way too many picks for not enough success.
But to me if you're letting your GM go, then you want a new vision and you bring in someone to give them a chance to make the team over. Sheldon Keefe was in his last year of his contract, a new GM just got hired, wouldn't it make sense to let the season play out and see how it goes? Refusing to even consider trading one of the Core 4 and announcing it the world was also dumb. I love Nylander and I think the deal he got was fair value, but the problem is, the Leafs couldn't afford it. There are no goalies, the defense is extremely shallow and there's no secondary scoring.
There's a lot of talk about how the Leafs don't win because they're too soft. I don't think that's the main issue. The fact is that in the playoffs, the opposition has more leeway to defend against the Core 4 aggressively. There's no threat from the bottom 6 of lighting up the lamp. Just adding goons won't fix that problem. The new deal for Matthews shows that it doesn't matter who the GM is, the players hold all the card. Auston got exactly what he wanted and didn't have to make any concessions this time either. JT can't be bought out (no cap savings) and can't be traded unless he waives his NTC and even then, what are you going to get for him?
Lou is gone, Babcock is gone, Dubas is gone, the only one left who has been there since the beginning of the "rebuild" is Shanahan. If the Leafs fail again, he's the one whose head's got to roll. With Nylander's new deal, the Leafs are stuck in cap hell for the foreseeable future. Unfortunately the only thing they can do is keep their draft picks and try to find a pearl in the draft. They can't sell, they can't buy and at the end of the day, everything that happened was signed off by Shanahan. Even if you want to blame Dubas (which isn't unfair), now Shanahan has fired his last bullet. He just extended the coach, firing him would just reflect extremely badly on him.