Frost and their 1st rounder for a 1 year rental of Trouba (he won’t sign a long term contract for many reasons listed below) that’s way way too much for a rental.

Reasons why he goes to UFA:
1) Salary cap will go up next year means more $ for UFA's
2) Every team can bid and not have to give up assets means more $ than by choosing among the few that met the Jets trade demands. Also means he gets a true choice of where he goes.
3) Expiring contracts means teams have more money than before
4) More info will be available about the upcoming CBA so he can structure his contract as lockout proofed if necessary
5) He gets to stick it to Jets management for their role in the failed negotiations that lead to his holdout, for denying his 1st trade request in 2016, for taking him to arbitration in 2018, and for putting him on the block right now.

The same reasons could have been given about Stone yet he still signed longterm before hitting free agency

Ottawa was not a cup contender and stone was traded after the following year’s cap number was known (trade was in February so It was only a few months earlier than free agency) and it was to a playoff team. Not 13 months when the cap is unknown. Plus Ottawa’s management didn’t screw him over like the Jets management has with Trouba.

Apples and Oranges comparison.

1. The cap for next year hasn't even been officially set yet we are all just going on an estimated assumption
2. Stone may had bben traded but that didn't mean he had to re-sign with Vegas instead of testing free agency
3. The Jets management didn't screw Trouba over, they just weren't gonna let Trouba just screw them over. We originally wanted to sign him longterm, Trouba just doesn't want to play for Winnipeg, and just because someone asks for a trade it doesn't mean you have to send them away right away instead of taking time for a reasonable offer to be made.

When Stone was traded the cap for the following year was estimated to be $83M a prediction Gary Bergman made on Dec 3rd. Don’t believe me? Read here Comparing that to today where ‘20-‘21 is unknown. (Apple to Orange).

That increase meant teams had another 4.4% to spend.

2) Again Stone was 4 months from being able to fully negotiate. Not 13. And Stone was on a sinking ship that could devalue his payday. Trouba is not. (Apples and Oranges) Knowing what the cap will be meant that his agent could fully negotiate a long term deal without leaving money on the table because the team could have it’s capologist crunch the numbers.
3) Yes, Jets management screwed him over. He won his arbitration case against them. That’s not a fun process. Jets went cheap and were told so by an independent body. In addition, their negotiating caused him to holdout and then request a trade publicly. That doesn’t happen if the relationship is good. It wasn’t just over the course of the last deal, this goes back years.

But if you want me to put it another way: Trouba will not do Jets’ management any favors on his way out the door. Is that worded to your satisfaction?