Yeah that's what I think has happened to Matthews a bit. He's had some injuries, and some personal success, and is viewed as a superstar, so maybe he has taken his foot off the gas a little. He's not driven to be in the same class as McDavid and MacKinnon. He's happy with what he's accomplished, and now he'll show up, play some games here and there. Every so often he'll show flashes of the player he used to be, but he is not going to be dominant. He's not going to grab this team by the collar and tell everyone they can't have sugar anymore. Just not his nature.
You don't necessarily need that either, if your team is strong. You can get by with someone who is pretty good, as long as lines 3 and 4 don't have a drop off. But the Leafs don't really have that. Florida sure does though.
I believe that originally the Leafs were built around the Pittsburgh Penguins model that won the cups in 2016 and 2017. The forward lines on those teams just overpowered teams. You had Crosby, Malkin and Kessel coming at you. Sometimes on one line, sometimes on three different lines. They got timely goaltending. Their top d-man in one of those runs was Trevor Daley (Letang was hurt). In order for that model to succeed though, One of Crosby, Malkin and Kessel had to be unstoppable. I think when the Leafs had Marner, Matthews and Nylander, they looked at their talent and they said "Yeah we can do that.", but it didn't really work out that way because they never wanted to break them up. They always wanted to have the three of them playing on the first two lines. I think this meant that they couldn't work the matchups the way they wanted to, or at least the way that Pittsburgh was able to during those runs. Also, in the playoffs, Matthews, Marner, and Nylander became stoppable, so that side of it didn't work either.
Now Marner is gone, Matthews is a shadow of his former self, and Willy's going to Willy when Willy wants to Willy, but that won't happen sometimes because the other team won't let Willy Willy when he wants to Willy.