Zadorov is basically a career #5 guy, and was a UFA when he signed his current 2 year deal. I tend to like to estimate high on UFA's but I don't think he's making anymore than he currently is, let alone $5M.
In general though you really wouldn't call the defense 'rebuilt' with all the UFA's, but rather Allvin has proven himself competent in constructing a blueline for the season. Something that only seemed unachievable because we got used to our GM spending all his salary and assets on Sbisa/Gudbranson/Myers/OEL.
Most of his career he has been on teams that had established defence as their core players so cracking the "points" was harder for him, also that he has been looked at to be a one dimensional type player.
While 5 million might be too much now if 3 years it could be a bargain especially if he does develop into a reliable 3/4 guy. Large defencemen often have longer careers too.
If Allvin can fit him to 4.5 to 5 mill that is less than Myers present 6 and Zad does adds more to the physical game. Maybe match him up with Hronek.
The last million of Myers cap hit and Cole's 3 million could/would be used in signing a FA, Cole, Tanev, Myers.
There is a minute possibility he has an inner Hedmon, Hamiton or Eckblad that just needs opportunity. He is supposed to be a superior skater.
This is a "hockey" trade to me, not just a rental.
And I believe the team does need to add another top 4 dman, a place holder for one of the young prospects to fill in 2/3/4 years.
My preference is likely close to Tocchet's or his closer to mine. Long ago while selecting the WJ national team there was the comment of, "we prefer players that duck to get through the door unless like this guy (showing a picture of Gretzky), we can teach skating."
So "my team" starts with being bigger than league average size with exceptions for super high skill, but if two players are close then size is a major deciding factor.