All these guys together form one of the worst defenses in the league, and even in the AHL, their performances aren't stellar.
I don't think they're undervalued.
My assessment takes into account the role these players should play at their full potential on a title-contending team. If Vlasic and Levshunov are Chicago's first and second defensemen, fine. But with that, it'll still be a team that's playing the lottery to get the first overall draft pick. Alex Vlasic, in Montreal, he's in the top 6 behind Hutson and Guhle. And Montreal is only an average team in the league.
If this group is to move up a level, it will not be with these guys but with the addition of talent.
They are one of the worst defenses in the league. They are also all 23 or younger.
To put that age into perspective, the Western Michigan team that played and won this past Thursday had, on average, an older blueline than the one the Hawks iced that same night. Literal college teams are icing guys older on the backend than what the Hawks are. It's not at all surprising this is one of the worst defenses in the league.
Levshunov has done fine in the AHL this season. Point totals weren't that impressive, but he was the 2nd youngest player in the A this year and the overall youngest defender. As I said previously, he was 3rd on sog in that entire league at the time he was called up, and he did so as a D+1 player.
And your assessment had Vlasic as merely a "top 6" guy. Maybe he's not amongst a contenders top 2 D, but he sure as hell isn't just an NHL level defenseman. He's at least a middle pairing guy on almost every contending team. Again, he's top 60 in points, despite being a shutdown D, and is playing over 23 minutes a night.
You mention that Vlasic would be on the 3rd pair in Montreal and I'm not so certain. He's got a higher PPG this season than Guhle and averages over 2 minutes a game more. Maybe you can make an argument that Guhle is better defensively, but I'm not even sure of that. Vlasic is highly touted for his defensive play, and like I mentioned in my previous post, was considered by The Athletic as the 2nd best pure shutdown defender in the league last year. Even if you want to come to your own conclusions about how to judge a player for their defensive abilities, it still says a lot about how good Vlasic is on that side of the ice. I will also say that Vlasic was probably a bit better defensively last season, but not by some extreme degree.
And even if you still wanted to have Guhle in front of Vlasic, that doesn't necessarily mean Vlasic would be a 3rd pair D. Would you say Drai is a 2C because he plays behind McDavid? Was Malkin only ever a 2C because he played behind Crosby? Not to mention that Montreal being a mid team this year isn't necessarily because of the talent of their left side D, that's really not how it works. Teams can have amazing depth in one position and be weak at other spots in the lineup.
And I'm not even advocating that the Hawks have the best future D core in the league like the OP did. I think most of their strength will be on D and I think there are guys with the potential to become 1Ds in this league, but guys having potential or hitting on said potential are too widely different things. I simply like the potential and the fact the majority of those guys are 6ft2 (or taller) and are, for the most part, good skaters. Makes for an exciting group.