There are so many ways Arizona could get younger on the blue line without trading away their much needed 2nd round pick for an average defenseman on an albatross contract. Ryan Murray got traded this offseason for a 5th round pick, he's a UFA and a better option than Matheson. There's Brandon Montour too. Ain't anyone giving up a high pick for Matheson.

A. I think you under rate Matheson.
B. he's not a rental, he's coming with term. And as much as you view that as bad, it's not.
C. I think you are over estimating the Defense market next year. The league is already very thin at defense in general. there are many teams in need of it. Next you get 6 more defense positions are opening up, making the league even thinner. And Seattle is gonna grab defense from a few teams. Which means whatever else is out there, everyone else is going to be over bidding on.
AZ is in the same bad position as DET. Who doesn't really have a lot of defensemen going into next year. They need to get younger and faster.
Finding that many defensemen to improve is not going to be easy in the current climate. That's just something you are going to have to realize.
This is why Gudbranson kept getting moved when everyone wanted to hate on him. The league is just thin and that is going to get worse.
Matheson is a much better player than he was. He went for a 5th this summer. Matheson should probably return a 2nd as he can actually play 2LD and that is roughly what a low end 2LD costs. Where a higher one is going to cost a 1st +.
So the value here really isn't off, and AZ won't have nearly as easy of a time picking up defense next year unless they want to go with their very old players.

The leafs absolutely do not need bottom pairing defenders

Coyotes need RD not LD and as mentioned above they’re not giving up a second round pick for Matheson

Ceci isn't worth anywhere close to a 4th and the Jets have no need for bottom pairing or lower defensemen.