Tre was in a difficult spot in Nylander negotiations due to that backstabbing little turd that preceeded him making him need to rush to make a decision IMO. It's still a bad contract but it's a little more understandable. Plus, some may disagree but I'd take Nylander in the playoffs over Marner.
Marner's situation is different. You absolutely cannot have two $11M/year wingers that don't dominate in the playoffs and expect to win anything in the Cap era. The die should have already been cast for Marner the moment Nylander's contract was signed.