I think the $10m number is a bit arbitrary, and the theory has worked out of more randomness (in part due to lack of players as you state). A .number of teams heavily commit to the core - the uniqueness of the Leafs is the lack of diversity positionally amongst that core.In fairness, there aren't a lot of players who make that kind of money. For example here are the players that currently make $10 million or over per season
Connor McDavid $12,500,000
Artemi Panarin $11,642,857
Auston Matthews $11,640,250
John Tavares $11,000,000
Mitchell Marner $10,903,000
Aleksander Barkov $10,000,000
In 2023-24 Nathan MacKinnon will become the new highest paid player in the league with an AAV of $12,600,000. He was making $6,300,000 per season when they won the Cup.
Tampa Bay has 3 players that make $9,500,000 per season - Nikita Kucherov, Brayden Point and Andrei Vasilevskiy. Two others make $8,500,000 - Steven Stamkos and Mikhail Sergachev. That's $45,500,000 tied up in 5 players.
Regarding the Leafs.
Nylander's contract is fine.
Matthews $amount is fine -- the awful part was the term that Dubas gave him.... just terrible negotiation on that by Dubas.
Marner is a very good winger -- but as a winger he is overpaid by a $1-2m
The big issue was Tavares contract. Tavares is a good player, but you can spend it more wisely on diverse players. Leafs could have been stronger team with using the Tavares cap space another way, and would have been able to win with a $10m player.