It almost never happen for a less .600 team to win the cups, the Kings did it in 2011-2012, yes like Vegas any team with a .940%+ save percentage goaltender with a bunch of overperforming in the playoff players can win series.
There is definetyle a concept of windows of significant opportunity of winning the cups outside some freak luck/goaltending performance occurring.
Last year Capitals had a .640% team, first in their division, +20 goal for, with 4 stars skater and a vezina goaltender going .922, Orpik was the only Washington player over 32.
Ov: 32
Backstrom: 30
Carlson: 28
Holtby: 28
Kuznetsov: 25
That was not a closed windows.
Take the post-lockout Det RedWings has a clear example of a team with a good windows that closed up or the Canucks in the 2010s or the Leaf building and entering one this very year.