So what are your chances of winning a cup with the best defenseman in the league, as opposed to the #5 defenseman in the league? I'm sure they're better, but not by that much.
Since the first lockout, here are the teams (OTTOMH) that didn't have a Norris-quality d-man on their team:
1996 Avalanche (Ozolinsh/Foote)
2004 Lightning (Boyle)
2006 Hurricanes (F. Kaberle)
2009 (barely, with Gonchar/Letang) and 2017 Penguins (Schultz)
2019 Blues (Pietrangelo, again borderline)
2023 VGK (Pietrangelo)
The Avalanche had Roy, Forsberg, and Sakic
The Lightning had Khabibulin, St. Louis, and Richards
The Hurricanes had Eric Staal and Cam Ward
The Penguins had Crosby, Malkin, arguably Gonchar, and later Kessel
The Blues had O'Reilly
The VGK had Stone, Eichel, and, arguably, Adin Hill given his performance in the playoffs and this year.
You can go back even further, and since WW2, only the 73-75 Flyers and the 1993 Canadiens don't have a Norris-quality defenseman.
So if you want to win without a Norris-quality defenseman, you better have superstars elsewhere.