From the outside, that’s how I viewed him. A guy that you’re pretty sure is an NHLer who passes well but doesn’t defend to a level you’d need from a guy playing a lot harder ice time.
That can be learned sure, but it’s hard to put all of your eggs in a basket for a guy like that because there’s quite a few guys that fall in that category. He doesn’t seem to have any exceptional skills but is an above average passer.
In general you're right, but Barron has a couple other "+" skills to go alongside his passing ability. Though nothing truly elite mind you.
One of the things that jump out at you when you watch Barron play is how good at holding the blueline, skating with possession along the line while under pressure he is. Then there's also the fact that Barron's ability to find/create a lane to shoot from the point is also very, very good, as evidenced by his 6 goals in 36 games this year despite limited minutes on the powerplay, an anemic offensive team, and not too many minutes overall.
Defensively is where he will need to improve most if he wants to be a true #3-4, as you've said.
In any case, the top 4 upside is definitely there in Barron's case, and seems reachable for him as others in this thread have said, but until he puts it all together it remains just that; potential.
All of which to say that though Barron tracks to be a good puck-possession defender with interesting offensive qualities to his game, he is also not developed enough right now to warrant a team investing massively in acquiring him.
Inversely, he also seems well-liked in Montreal, showing nice progression as a young just-turned 22 years-old defender in the NHL with some interesting upside to boot, so there's really no reason to trade him unless Hughes gets what he'd consider an overpayment for him.