You have rose tinted glasses on big time. The Leafs actually took the series lead without Kadri in the playoffs. Kadri plays no part in the team if he isn't playing for them during the most important time in the season. Kerfoot is a better fit for this team and he isn't going to take back to back suspensions and seriously hurt the team. Barrie is a perennial 50 point defensemen but sometimes a different system doesn't suit the player , it happens but that doesn't mean he's worse than Gardiner, who looked mentally out of it by the time he left anyway.
The special teams issues are more to do with coaching, than they are to do with personnel. The PP last season was 8th(22%),and PK was 17th(78.7%). This season, PP is 21st(16.7%) and PK is 25th(75%). That cannot all be down to Kadri,Gardiner and Brown's absence
Dubas has not destroyed the franchise, calm the hell down, you lose any credibility saying that stuff. Even the Bruins, Tampa and Nashville missed the playoffs while having strong contending teams. Sometimes that happens, but I still believe the team will make the playoffs , even if they regress to the wildcard.