Pastrnak's an absolute stud, but then so is Mitch Marner.
Marner also has the advantage of still having two more cheap seasons left on his ELC, while Pastrnak needs to be paid big bucks, starting this season. Marner also has six more seasons left before he's eligible to be a UFA, while Pastrnak only has four.
So unless you think Pastrnak's on a completely different level than Marner, and there's no real evidence of this---there's no point to making this deal from Toronto's end. As for Boston---I mean, goddamn, just bite the bullet and give Pastrnak his money. He'll be worth every penny of his deal, and eventually the Bruins need to stop dumping their young studs as soon as they turn 21 years old.