I would agree with the sentiment that Nylander is pushing his value because the league is starting to move toward paying reasonable contracts to productive young players, not just the absolute pinnacle of superstars. And even the more fair deals signed, have turned out to be massive bargains a couple of years in, so I think we are just seeing that evolve further in this case.
The big reason this has gone on is that this is a perfect storm. Nylander plays for a team where he is the 4th best forward the team has, and the other 3 will also all have contracts signed within the same 12 month span or so. That simply increases the financial stakes for both sides in this negotiation, and neither side is in a rush.
Contrary to popular belief, neither side is really losing anything. Dubas doesn't care what the cap hit is this year, and every passing day, the weird quirk in the system that moves more of the total contract to the first year, lowering the AAV later certainly isn't hurting him.
Also, for Nylander he knows he can get a large portion of his deal paid out in signing bonus in the first year, meaning the salary he is losing isn't nearly as big as people are speculating. It's more like $4500 a day if they pay him the minimum in salary and rest in signing bonus in year one, and since the Leafs will have no qualms on that part of it, that will not be something they fight over if it gets a deal done they are happy with.
It is what it is, a tough negotiation because he is probably the best player in the last decade to be in a situation where they were the 4th best forward their team had to sign to a deal inside of 12 months.
Not many teams have 3 better forwards, none of the ones that do had to sign them all in such a short time span.