Yeah that's why I never really got into the whole "sell high" on Matheson stuff. I think he's a pretty OK 2nd pair D who's uniquely well suited for the specific role of "#1 on a bad team to keep the puck moving so your forwards get touches" but I don't think anyone around the league would have been fooled by the 62 point season last year and I doubt his value has changed much or will be much different as a pending UFA either.
I just don't really think he ever really had or would have had that much trade value, a contender would be looking at him as a 2LD puck mover and a bad team would be trying to add him as a token vet to fill the #1/leader role and keep the game flow respectable for their forwards as a puck mover. Neither of those roles are really the kind of roster chair GMs are going to pay a ton to fill.
Muzzin returned a 1st and a couple B prospects, Ekholm returned a 1st, 4th, and a B prospect, just don't really see how Matheson's value would be in that ballpark since those guys are/were clearly better players.