No he isn't. The leafs achieved exactly what everyone expected them to achieve. They pushed a more accomplished, more balanced, overall better team to a game 7 and lost in the other teams rink. The Bruins are a better team statistically and their best players have won a cup. They are maybe the favourites to do that again right now.
The leafs have shite defence. Everyone knew that going into the season and that didn't change at all during the season. They aren't in their window of true contention yet. Their core players (outside of Tavares and Reilly) aren't even 23. They need another couple of pieces on d and more grit and grind in their third and fourth line. If Kadri is their enforcer, they have problems.
I'm not a huge fan of Babcock but letting him go right now is silly. Mgmt knows, the team knows and generally the fans know what this team is and that's probably 2 years away from truly contending.