It feels like you're trying real hard to create a narrative here. Chisholm has absolutely been a top pairing AHL defenseman for 3 years now and easily available stats aren't everything when projecting defensemen. Stats that aren't so easily available (and watching him) show that he's been elite defensively in the AHL. You're projecting him as if he's an offense only player which is incorrect.
No longer talking prospect D here, so just wanted to add that IMO relying on those often opaque and sometimes seemingly random AHL counting stats can be tricky when evaluating D prospects especially in that league.
As a D for the Moose you're often playing all over the shop in terms of pairings, setups and situations, and as a veteran being used to support specific FW groupings and players for evaluation and dev purposes -- there's no effort made by org or coaches towards making you look good or pounding out the point totals a la 2022-3 Karlsson. So if you're not watching the games you're not seeing the player really.
That's how some narratives can persist perhaps, like Chisholm as a "good in the A and that's it" player, or Heinola as a meek and non-combative defender who shirks contact and is unable to dictate play, etc. I can't get the AHL reliably over here, so didn't see much of Chisholm last season, but I've seen pretty much ever previous game he played with the Moose and along with Heinola he has been one of the league's elite for years now. He channels play, is strong defensively and versatile on special teams and plays an excellent, steady mostly error-free game that likely translates to the NHL in a manner that's not dissimilar to Samberg's, with less size but better skating and good offensive upside.
I don't see him as a middle-tier D in the AHL at any point in his career there and I doubt the scouts or org do either. And he is likely IMO a better D overall than Stanley, who has height, or Capo, who lacks top-end skating and IMO thinks the game more slowly from what I've seen of him.
I still Heinola is the more brilliant but also riskier defender. But in the end the Schmidt and Pionk contracts, plus the extra year for Capo The Good Solidier and Stanley signing mean that it's back to the AHL certainly for Heinola and probably for Chisholm, unless Stan is traded and/or Capo waived. And if I'm Chisholm I'm doing everything I can to force a trade to an org where there's an opening before it's too late.
I really don't see this logjam as about our D prospects' failure to launch -- no one's "kicking the door down" with a few games a year and guaranteed benching / demotion if they make even an ordinary mistake -- something you see Pionk do 8-20 times a game -- because we all know there's no way Pionk gets benched even with 2 seasons' worth (at least) of play so embarrassingly bad that he's actively handcuffing the team, and the headache of Schmidt who can play well but is clearly vastly overpaid and overterm'd for what he's brought.
This is not a prospect problem. It's a Chevy / org problem and it's been in the making for years. Hopefully he'll figure it out.