Nah. Winning a cup is hard. We'll have to go through other very good teams who also have a game changer (maybe multiple). Like EDM with McDrai or TB with Kuch / Stamkos (maybe Point and Hedman) or TOR with Matthews / Marner or even PIT with Sid and Geno who are still game changers even now.
One game changer is not enough for a cup contending (let alone winning) team. The more game changers the better
I genuinely believe that Toronto as a team is very close to being able to win a cup, a little puck luck and better matchups would see them able to beat most other teams, the problem is that they never have these things, and that they play down to other teams and other teams play up to them. The other thing is that they always have super bad matchups in the playoffs like Tampa, who are essentially the Leafs but better in every way, having a franchise goalie, a much much better D corp headed by a better #1D, and at worst a slightly worse forward corp that plays much better in the playoffs.
All that to say that I hate the Leafs and hope they fail forever, but that Matthews alone would be enough if you add the rest of the team and have a good one around him with good coaching and a little luck. If Matthews is your best player that's certainly not a problem. And if the Leafs just swapped 2 of their second best forwards for equivalent goalie and D, they'd be at worst in the same spot they are now.
Hopefully we can follow that template in the future, because honestly it looks like our future is quite bright. And as long as Tourigny is the coach I have faith in him. Think about it, when the Leafs started this core with Nylander, Matthews, and Marner, they had much less depth than we do in the cupboards. They've attracted some free agents and made some trades, but their cupboards are still fairly bare, and they still have the same core they started with. Our current core is much worse, obviously, but our prospect pool? I'd argue that it's better now than it ever has been, as a whole- Keller and Schmaltz are good pieces. Chychrun is a good piece. Crouse is too. But we have Guenther, Cooley, Moser, Soderstrom, our 2023 1st, Geekie, and even other pieces like Doan, Macelli, Jenik, Raty, and Fedotov. Not all of these will probably pan out, but they all have a pretty good chance to do so, and if they do all pan out, in 1-3 years I think we'll have a great roster that can compete. Especially if we keep adding through the draft and FA while this is happening to shore up weaknesses. The ONLY thing we're really missing is elite pieces- we have a glut of talent at nearly every position (sans goaltending) coming up through the system, but we're lacking the elite Matthews like talent currently- although Chychrun could be that for us on defense. And our 2023 1st is HOPEFULLY going to shore that up so...we might just be set, hopefully.