Nylander has point a game potential and is 22, his contract will be the best on the team as soon as this season. Not an overpayment at all.
In the description, I stated that if Gardiner's back scares people away, and a bad back is never a good thing, it could prevent him from getting decent long term offers. At that time, it may make sense that he signs a one year deal with the franchise he's known since he entered the NHL and hopes to rebuild his value and get a bigger contract next season.
This is a huge hypothetical but let's say he can't pass a physical right now and still is in that boat in July. Who would just give him a 6 year 6 million dollar deal on a hope that his bad back magically fixes itself. He may need surgery, that's a major issue. Its possible that he only gets a smaller deal on the table from other teams. At that time he may rather bet on himself, stay in TO for one year and see what happens next year. This is the scenario this whole thing is based off of. You just flat out saying no, because he will get 6 million on the open market is just ignoring the very specific and reasonable parameters set forth.
As for Kapanen, no one is going to sit across from a negotiation table and say, I want 4 million or offer sheet time! If they did, their GM would say, okay well you haven't proven anything yet so we are trading you to the highest bidder and believe us there are bidders. Don't like that, then either be reasonable or good luck.
Then Kapanen has to make a choice, stay with this building club that is on the verge of being one of the most dominant teams in the league or have very little say in where you end up. All that being said, I think the Leafs trade him anyways. He'll get the most return out of the potential trade guys, (Brown, Kadri, Zaitsev, Johnsson and Kapanen are the potential trade guys) so why not move him for an elc that fits the needs of the team.