Odd results. I understand why people are hesitant to believe in the Leafs, but there are some other expected top teams with some pretty big question marks as well. It gets even more odd since most who mention them seems to base it on the Leafs having a tremendous offense but might be limited in how far they go because of their defense, which is pretty much spot on the general idea of the team. So it doesn't really feel like they should be a runaway favorite here.
I think my vote might go to Nashville. At first glance, they are the strongest team in the league. But before last season, Rinne was looking like a below average starter on the downswing of his career. I remember doing some statistical analysis mostly based on dSv%, and he ended up out of the top 30 altogether. Then he had a clear-cut Vezina season at 35. I wouldn't be so sure that it won't be an outlier when we sum up his career though. Add that their center depth seem weak compared to most other playoff teams, and that their overall forward depth seem rather weak and... well, there are more question marks than you think.
On the other hand, if Rinne falters then they have a guy who should be a starter in my opinion to take over the reigns. And while the centers are overall a bit weak for a top team, Johansen really seem like the kind of guy who raises his game when faced with a true challenge.
Summed up like that, I don't know if I would even call them overrated. Just a team with question marks, which is true of pretty much everyone this year. Can't think of a better example though. Maybe the Islanders? To me, they seem like a team without much talent outside their top 10 center.