How so though? I mean, nobody in the NHL makes more than 12.6 (which MacKinnon just signed last summer) so how does Matthews warrant 13.5 when his numbers aren't better than MacKinnon, Pastrnak, and Tkachuk, let alone McDavid or Draisaitl.
Matthews' numbers (which doesn't even include his defensive superiority) are better than these player's numbers when you look properly at a relevant sample through time of signing. The only exception is McDavid, and McDavid's post-ELC cap hit percentage after giving one of the biggest discounts in cap era history is still going to be bigger than Matthews' UFA cap hit percentage. And when McDavid signs his UFA contract, it will also be more than Matthews' UFA contract.
David Pastrnak just signed for 8 x 11.75 and scored 60+ goals and 113 points this season (7 more than Matthews best).
Nate MacKinnon just signed for 8 x 12.6 and scored 111 points in 71 GP this season (after just winning a Cup).
You're looking at a full season of Mackinnon and part of a season of Pastrnak that have zero relevance to their contracts, because it happened after they signed their contracts. That's not what they're being paid for. That's not what formed their contracts. Contracts also aren't just based on one peak season. Somebody like Mackinnon's raw points are also going to be comparatively inflated because his team spends so much time on special teams, but that doesn't make him better. Teams aren't paying a player for how much time the team has recently spent on the PP. They're paying for the player's ability to generate production in that game state, which is comparable to Matthews.
Meanwhile, Matthews is a better 5v5 producer than anybody in the history of the cap era that has signed a currently legal contract.
Looking at the names you mentioned over the 3 years prior to signing:
Matthews: 67 points at 5v5 per 82 (while playing injured for 2/3 of his sample)
McDavid: 65 points at 5v5 per 82
Mackinnon: 61 points at 5v5 per 82
Draisaitl: 55 points at 5v5 per 82
Pastrnak: 51 points at 5v5 per 82
Tkachuk: 48 points at 5v5 per 82
Why are all of these supposedly better and more valuable and healthy players not able to produce like an injured Matthews in the most equal and common game state by far?
That's not even factoring in the overall 5v5 impact, where Matthews separates himself even more with his defensive play.
Now, McDavid is arguably the best PP player ever, while being pretty close to Matthews at 5v5. That's going to launch him above Matthews. Draisaitl also produces better on the PP... but that's hard to fully attribute to Draisaitl with him playing with the best PP player of all time... And the gap between them at 5v5 is pretty massive.
The rest (Matthews, Mackinnon, Tkachuk, and Pastrnak) produce at a similar normal elite rate on the PP, so we're left primarily with the gaps between them at 5v5.
But they want to completely ignore the negative:
1. Big dip to 85 points last year
2. 0.88 PPG in playoffs
3. Scoring at a 36 goal pace over 82 GP in the playoffs
4. Only able to win 1 round in 7 years with him being overpaid as it is
5. Wrist injuries
6. Only one 100 point season in his career
Nobody is ignoring "negatives" or concerns. We just recognize what actually factors into contracts, and the context that makes some of those statements misleading.
It basically comes down to two concerns - injury history, and career playoff production/team outcomes, but those aren't things that meaningfully impact contract valuation.
Injuries are what they are. They suck, they're concerning, but anybody can get hurt. He's already contractually hurt by playing injured in 2/3 of his recent sample. You can't just then randomly knock even more off because you wanna. You'd have to not sign one of the best players this franchise has ever seen because he's been injured before, which is obviously not going to happen. You just have to trust that the Leafs are well-informed about his health moving forward, and hope he stays healthy, like many teams have before with their franchise players.
The playoff production is largely just misunderstood, as the differences there are more a result of discrepancies in the situations faced and experienced (which vary massively across teams in the playoffs) than discrepancies attributable to the individual. Teams and players know this, even if some fans lag behind accepting it.