Nobody said its mostly dumb luck, but some outcomes are more luck based than others. The accepted percentage of outcomes that are defined more by luck that controllable outcomes within hockey tends to be quoted around 25-35%
Why it’s so much harder to predict winners in hockey than basketball and
Percentage Luck in Hockey, Explained for some further reading, there are others as well that I've read that I'm not going to waste a bunch of time digging up. There is actually a fair bit of research on the topic.
Whatever the % of outcomes you attribute to luck, whether you think its on the low end at 15-20%, or at the high end at 40-45%, its still a pretty large number for hockey. For every 10 series that are played in the playoffs, 1-2 of them on the low end will be determined primarily by the "luck" that happens in the series (bounces, deflections, shots hitting the cross bar, fluke goalie saves, flubbed shots, bouncing pucks, weird ref calls, etc etc). The reaction isn't "oh we are going to be beholden to luck for X% of the time, so why bother", but rather to just admit as fans that sometimes your team is going to lose when they should win, and vice versa. It's just part of the sport.