Demelo is not a top 4 D he lacks toughest and is not a top puck carrier/skater like Josh and you need one of those trades to be a top 4 but hey he wanted to stay in Winnipeg so can't complain too much.
It seems to work with him and Morrissey and Scheif's line from time to time, better than any other defensive combination, and De Melo is mostly the guy who holds the line, keeps pucks in front of him. Foot speed when the big guns aren't skating will get exposed, but for some reason this combination of defense and forwards is the best one the Jets have for generating goals. I'm sure the stats support this.
De Melo's a fringe top 4 player, but last year's regular season success was no fluke. I think it's chemistry that the Jets work on. What changed in the playoffs, and I am not sure who made the decision, was to match up Morrissey and Melo against Mackinnon with Lowry's line, and have Pionk and Dillon/Samberg behind Scheif's line. Neither combination was overly successful, and that may get revisited, but Samberg and Pionk are probably not the ideal shudown pair either, as Pionk is wildly variable in his outcomes. Maybe not physical enough either. Miller is physical, but not a puck mover. Or a regular special teams contributor, so he's another rung down.
I wonder if the Jets take a look at Ceci for the deadline. Probably not the same top 4 d-man who went to game 7 Conference final paired with Phaneuf in 2017, took a lot of heat last year for being a weaker link, with Nurse. But he's battled tested, can kill penalties well, which is a role Pionk hasn't excelled in for playoff time. And can move around the lineup more than Miller.