For perspective: 31s career playoff numbers are 0.07 & 0.04% lower than his regular season GAA & sv% respectively (2.46, .918 vs 2.53, .914).
All you can ask of any player is to maintain production level between regular season & playoffs
NYR series 31 posted a 1.86 GAA with a 0.933 sv%. In this era those are very good numbers for a goalie. Essentially Habs couldn’t average 2 goals per game or they’d have won the series. Had his 1C been a slight upgrade to Zibanejad or Stepan from Danault, I’m willing to bet he’d have won the series.
Goalies cannot outright win series in this era, IMO, I would agree they can keep it close or outright lose them, but it’s offense that wins series in this era where you need to avg at least 3 goals per game to make it to the finals let alone win.