This massively undersells the difference. Soucy would have been playing bottom pairing minutes on all of those teams but is this team’s third best defender. Guys like Cernak, McDonough, Bouwmeester, and Byram were all playing like 2/3 defenders when their teams won the cup.
Vegas is closer, and I can seem more room for disagreement, but I’d take any of their 3-6 defenders over any of this team’s 3-6 defenders for a single playoff run.
Can you win with a defence like this team’s? Yes. But it would be a ~25%ile or worse defence in the last 20-25 years and is definitely the weakest point on this team right now.
Looking at lineup on dailyfaceoff.com, I don't think we are significantly worse than any of the other cup contenders.
Avs: Makar, Toews, Girard, Manson, Byram, Malinski, Jack Johnson
Canes: Slavin, Burns, Skjei, Pesce, Orlov, Chatfield
Stars: Heiskanen, Harley, Lindell, Hakanpaa, Suter, Lundkvist
Oilers: Ekholm, Bouchard, Nurse, Ceci, Kulak, Desharnais
Panthers: Forsling, Ekblad, Mikkola, Montour, OEL, Kulikov
Rangers: Fox, Miller, Trouba, Lindgren, Schneider, Gustafsson
Lightning: Hedman, Sergachev, Cernak, Raddysh, Perbix, De Haan
Knights: Pietrangelo, Theodore, Martinez, McNabb, Whitecloud, Hague
Jets: Morrissey, Demelo, Pionk, Dillon, Schmidt, Samberg
Canucks: Hughes, Hronek, Soucy, Cole, Myers, Zadorov, Juulsen
Aside from the Canes and maybe the Knights, I don't think we match up too badly with any other team. Our top 2 of Hughes/Hronek is better than any duo except for maybe the Avs. Some teams might have a better #3 than us, but our #4-6 of Zadorov/Cole/Myers is better than most of the other teams #4-6. That also doesn't take into account that some of the other team's players are playing below their expected level this season, so while their roster might look better on paper, they are not performing as well as expected.
In a capped league, every team is going to have holes. Sure one or two injuries on the blueline can sink us, but you can say that for every other team as well. Luck plays a big part in winning a cup. I don't think many teams have a deeper blueline than the 2011 Canucks (arguably 5 top pairing D plus a very good Tanev ready to step in), yet even they aren't deep enough if you run into extreme bad luck.