The thing is when Dubas signed the players to those deals, they were looking great. Marner was coming off a career high season, Matthews is still worth his contract even if he's off to a slow start and Tavares was great when he signed. Conversely Nylander's contract was roundly criticised when he was signed and now almost everyone thinks he's a bargain. See how quickly things can change in a season or two? Everyone wanted Willy gone keep Marner and now everyone wants to trade Marner and keep Willy.
Who knows maybe by the end of the season people will like Marner again and if he shows up big in the playoffs assuming the Leafs make it there, then people will definitely be back on the love train for him.
As for Dubas I don't see many moves he's done that I really hate like I have with previous Leafs GMs.