Your statement is incomplete. Nobody is saying a 24 year old PPG player is bad. Or that a 24 year PPG isn't worth a ton of money. Of course he is. He is worth a ton of money. He is great, even though he gags in the playoffs.
Is it worth 11M per year?
Probably. But value is all about production minus cost. His production is not substantially higher than 11m per year.
I don't think Marner is worth $10.9 million dollars.
But let's say he is.
The debate isn't whether Marner is worth $10.9 million dollars. The debate is whether it is smart having a $10.9 million dollar player as the 3rd highest-paid player on your team.
Compare it to building/buying a home, and you have a limited budget (similar to how a salary cap limits your expenditures).
Is a $5000-$10000 massive-screen TV worth the money it sells for? Maybe it is.
But what good does it do you to buy that TV when buying that TV means you don't have money in the budget to buy a bed, a refrigerator, and an oven/stove?
No team has ever won the Stanley Cup with a player making $10 million or more. Yet Toronto has 3 players making $11 million or more. * (I have rounded Marner up from $10.9 to $11.0, because it basically is the same thing) *
Toronto has 3 of the top 7 highest-paid players in the NHL. This is completely absurd. Especially when 2 of those players (Marner and Tavares) aren't even close to being in the top 7 in terms of talent or impact. If those 3 players were McDavid, MacKinnon, and Matthews, then maybe it wouldn't be as bad as it is. That is still no way to build a Stanley Cup winner, but at least it would be understandable. But Marner and Tavares being in the top 7 in terms of NHL salaries? That is way overpaid and overvalued.