Colorado was 6th in GA per game and 2nd in GF per game. They didn't play anything close to one of the most defensive styles in the league and their forward group is not full of elite 2 way guys. MacKinnon, Burakovsky, Kadri, Rantanen, Landeskog, Donskoi, Compher, Nichuskin, and Calvert is not a top end defensive forward group, so I don't think we can act like they suppressed scoring so well due to the forwards' defensive play. They accomplished this despite the general consensus being that goaltending is the biggest weakness on their team and in the summer they upgraded Zadorov to D Toews.
I like the Lightning's top 4 a bit better than the Avs, largely because Hedman is the best player in the group. But their top 4 edge isn't enormous and is noticeably outweighed by Colorado's substantially better depth. Tampa's #5 D man this year is either a rookie or a 30 year old Jan Rutta who has 127 career NHL games played. He's played fewer than 40 NHL games in each of the last 2 years and isn't especially great at any specific skill. Their #6 D is either a rookie or Luke Schenn, who has played on 6 teams over the last 6 years, has played fewer than 30 NHL games in each of the last 2 years and somehow found a way to be -8 in 26 games with the Lightning last year. Cal Foote and Andreas Borgman might steal jobs from Rutta and/or Schenn, but plugging guys in with zero NHL experience is a big question mark compared to Colorado using guys like Erik Johnson, Devon Toews and Ian Cole in those lesser roles. The loss of Shatty and (to a lesser extent) Bogosian is not trivial since they are being replaced by rookies and/or guys who are barely NHL caliber players that they weren't comfortable relying on last season. An injury to any of Hedman. McDonagh, Cernak or Sergachev makes this group pretty darn average and even when fully healthy they just lack depth in the 4-6 D men. While I would take Tampa's top 4 over Colorado's this season, that advantage is outweighed by Colorado's incredible depth.
I have the Stars ranked as my #2 defensive group in the league and it is close. I'm not going to strenuously argue with anyone who would take that group over Colorado's because they are the clear 1-2 with a noticeable drop to #3 in my opinion. I have Colorado ahead of them because I think Esa Lindell is a touch overrated and the defensive group as a whole was caved in during the playoffs. They were 16th out of 24 in goals against in the playoffs this year (13th of 16 teams that made it to the traditional tournament). Khudobin sported a .917 in the playoffs, so it isn't like they just got awful goaltending. They were the first team to make it to the Final allowing 3+ goals a game since 1993. Again, I still think they are an extremely good group, but I think that playing in front of a top 3 tandem in the league props them up a bit more than people want to believe. Their team SV% for the last two years has been .924 and .929 in the regular season.
I don't love the Columbus group. Jones is an absolute stud and was a minutes monster in the playoffs. Werenski is good offensively, but has his own substantial defensive issues. Ryan Murray was awful last year, I like Gavrigov and David Savard is fine. The rest of the D is rounded out by a bunch of guys that they didn't trust to play 16 minutes a night. I think Torts makes blue lines better than the sum of their parts and there is zero question that the Columbus forwards do substantially more heavy lifting defensively than Colorado's.
Carolina has an amazing 1-2 punch in Slavin/Hamilton, but a drop off after that. Pesce took a step back in a bigger role last year from his awesome 2019 season. Eddy was their #4 D man most of last year and they let him walk. I think Brady Skjei is one of the most overrated D men in the league and Gardiner was pretty brutal at 5 on 5 last year (13 even strength points and -24 despite getting heavily sheltered minutes). Haydin Fleury should round out their healthy D group this year. He is developing at a good trajectory, but nothing about his game wows me. I don't think he is ready to be the 4th best D man on a contending roster and I think he has to leapfrog Skjei/Gardiner if that defensive group is going to be truly elite.
Nashville has a good top 3, but the bottom 3 is some combo of Borowitzki, Benning Fabbro and Tinordi (and maybe Yan Weber who is on a PTO). Boro is solid, but Fabbro looked outclassed in a top 4 role last year, Tinordi is a 27 year old who has never played 30 NHL games in a season, and Benning struggled to stay in Edmonton's top 6 last year. Like many other teams, the D gets real thin real fast.
I'd take Colorado's D over all those groups (although Dallas is close). Besides Dallas, every one of those groups has at least one major hole and a 3rd pairing that very much looks like a 3rd pairing. Colorado's 3rd pairing is a 2nd pairing on at least 10 NHL teams. Potentially more depending on which of Graves/Toews/EJ/Girard gets paired with Cole. There are more quality defenders in their group than any in the league and despite being an offensive guy, Makar is without question a legit #1 NHL D man. I genuinely don't get this narrative that the goaltending is the weakness AND their D is overrated despite them being 6th in goals against last year and improving the blue line in the summer.