A case could be made that a young and rebuilding team that has had a decade+ of futility finally breaking through and showing unexpectedly well for a playoff round or two is some partial degree of success. Toronto exceeded expectations. Even if Edmonton bows out in the second round, this season is a marked positive sign towards them moving in the right direction.
Boston hasn't rebuilt. Most of their key players are 30+, their captain is 40. That future gets darker before it gets brighter. Scraping out two wins against a not-great Ottawa side is no success.
A season in which you're so bad your team stopped responding to one of the most revered coaches in the league and upon firing him your age-old rivals hire him and proceed to win the division... meanwhile your team barely scrapes into the playoffs but makes a hasty exit without even winning a single home game... it is undeniably a failure.