What tells you that Carrier is a bottom pair defenseman, this is not your first time saying this. He's pretty much averaged 20 mins a night his whole career with practically no PP time. The guy was paired with Ekholm and tasked with tough matchups on a competitive team.
People also mention Fabbro but there is a reason that Fabbro's role was actually decreasing over his time in NSH while Carrier's was increasing despite the draft pedigree.
With Reinbacher's injury, Carrier will be a main stay in top 4 for the next 2 years minimum which is actually a bargain at his price. Fabbro looking good out of NSH shows how much of a bad work the staff is doing there so I think it's fair to think this year was the outlier for Carrier.
It's a new system for him, so I'd expect him to be caught in the wrong spot here and there.
However, hes been beat and rather easily on plays that doesn't matter what system you're playing.
He played higher/high up in Nashville because Nashville was never that good to be considered a cup favourite.
Fabbro in the two games against the Habs since his move has looked like a solid waiver pick up, nothing great, but that's two games.
Habs still have over 7 mill in cap space, so still a lot and will have more to sign free agents and/or take on cap dumps for more assets.
The Habs needed more stability on the backend to help their young d and to help the goalies. Barron sucks defensively, so Carrier is an improvement. Pretty much everyone else.
Losing that 2.5ish mill cap space sort of sucks as it limits what the Habs can do.
Getting another top 5 pick is needed for the Habs, but at the same time if the players just see loss after loss after loss the Habs will be in the same situation that Buffalo is.
So, losing a bit of cap space to help solidify the d-core and hopefully help keep games a bit closer and win some to help create a winning mentality is a positive.
At the stage the Habs are actually at, this deal is fine and potentially next dead line they can retain on Carrier and get some assets back to add to a deal for an upgrade/send him as a retained player even as early as this offseason in a deal for an upgrade on Right d.
What I'm saying is your team isn't a cup contender if you have Carrier as a regular in your top 4, but the Habs aren't even in contention for the playoffs, so this is more than fine