I've seen these arguments against Matthews quite frequently, but I honestly don't think they land.
$13.5M is only $900k more than Mackinnon AAV, and Mackinnon took a massive discount on his UFA price. Haggling over a million here or there with a player in the Matthews tier is missing the forest for the trees. You can save a million elsewhere pretty easily (e.g. don't sign Reaves). Even if it is an overpayment (I disagree), I'd rather overpay to keep an elite player than overpay Klingberg by $2M or something.
Also I don't think the Leafs should even want to sign Matthews long-term. 8 years? For a guy who's already had repeated/chronic injuries that are debilitating his biggest strength? It could turn out horribly.
As above, I think Matthews' profit maximization here is actually better for the Leafs too (in the short-term). I don't think the Leafs should want to go for a long-term deal.
I'm surprised Matthews is (reportedly) pursuing this route. If he gets a significant injury on his next deal, this plan goes up in smoke.