I have a feeling that in 2019 you'd be saying Devon Toews is not an NHL player simply because he'd been in the AHL up until that point. You know that thing about defensemen not figuring things out until about game 300? Middleton has played 345 pro games at this point. I'm basing my opinion on the 9 games he's played with the Avs this season, and in that time period, he's shown me that he's much better than Calvin de Haan, and that was while playing the right side as a lefty (and paired with CDH as well!). There's obviously nothing flashy about his game, and the offense isn't there, but he can clear the front of the net, intimidate opponents, make a decent first pass, and skate at least as well as CDH. Meanwhile, CDH appears prone to making absolutely terrible defensive reads despite him being a veteran NHLer. He's got a bit more offense to him, but nothing to earn him a roster spot. Kylington meanwhile looked great, but I don't think there's a spot for him with Makar, Toews, Girard, Manson, and Malinksi all able to move the puck well. What the team needs is a physical, reliable player to pair with Malinksi and kill penalties. That's Middleton until they can find someone better.
While I agree that the Avs should explore a trade for a better LD, until that point, they should see if Middleton can keep improving with more time on the roster. It would be nice to know if they can use him to replace some of what Manson brings long-term if there's another injury or they need to trade him.