This may sound a bit weird... but I think you highlighted why it was more of a success than a failure. Yeah they didn't win a Cup, but that was very unlikely from the start (there's a load management lesson in there)... but they had one hell of a season from a lot of different players and I don't think you can argue that they didn't do everything they could to send Bergeron and Krejci out on top. It didn't work, but damn if they didn't have a great season and they put their best foot forward.
The biggest one season failure in recent history to me is 18-19 Tampa. Great team, was playing very well, thought they had it wrapped up to only lose their mind and get swept. It just gets forgotten about because they came back to win back to back Cups.
Biggest one season failure in my mind ever though is 03-04 Avs. Nothing will ever hurt as much as that.