Lots of teams have one-off seasons or playoffs. It happens all the time. The fact that it surprises us is a failure on our part to look beneath the surface. There are concrete reasons why a team might succeed one season: Health, adding key players, development of young players, etc. Likewise, there are concrete reasons why the same team might fail the next season: Injuries, losing key players, aging vets, etc. There's nothing supernaturally about the final results over a full season /playoffs.
In Vancouver's case, they lost Demko plus other injuries, and they had pretty serious internal issues. They're not the same team as they were last season, and the results reflect that.
In Washington's case, they've added key players, Protas has taken a leap forward, and they have this winger who's been mostly healthy and scoring goals. Not close to the same team as last season, and the results reflect that.
Vancouver didn't overachieve last year. Washington isn't overachieving this year. Both teams have gone through big changes – for worse and for better – and the results accurately reflect it. The only things that overachieved were our lousy predictions and analysis.