It’s not off. And there are many ways to calculate it. Straight approach is just to calculate probability for the share of Canadian teams. 0.2/0.25/0.3 whatever. This is your yearly base probability.
You make it 1 - 0.25 (for example) and 0.75 is your yearly probability of not winning. To calculate it for 30 seasons in a row you should raise it to a power where the power is your 30 seasons.
(1 - 0.25) ** 30 = 0.00017858209017001. 0.000178 is probability of never winning for 30 seasons in a row. So this is basically impossible that no Canadian team was able to win.
Also, you can calculate it with # of teams who made finals if probability there is equal. 6 Canadian teams made it to the SCF. (1 - 0.5) ** 6 = 0.015625.
Etc.
You're overthinking it. Canadian teams make up 22% of the league. Taking out competence, ability and skill, statistically every year there is a 22% chance that one of those teams win the cup.
There are many groupings of 7 teams that have not won the cup in 30 years. Many.
Now, taking statistics out of it, up until the salary cap era, most Canadian teams didn't have the finances that Cup-winning American teams had. As a fan of the Oilers growing up and watching us play Dallas and Colorado every year in the playoffs in the late 90s/early 2000s, the Oilers team salary was nearly half of the aforementioned opponents.
It becomes a more fair question when speaking about the salary cap era and all teams essentially being equal financially. Quickly going back to statistics, 12 of 32 teams have won in this timeframe (roughly 63% of the league have not, keeping in mind 22% of the league are Canadian teams).
The biggest disadvantage I've noticed in the salary cap era is that the development of American players has quickly caught up to Canada and that we're seeing a larger percentage of impact/star players that are American born. The impact that this has on the league is the trend that most of them avoid playing for Canadian teams when given the opportunity. As an Oilers fan, the pool of players that we have the opportunity to acquire as a contending team is simply smaller than our American competitors knowing that the Brett Pesces and Patrick Kanes of the league would never play north of the border. Yes, I know there are American players that have bucked the trend, but there are many more examples of players that I'm talking about.
The other challenge I've seen is the cronyism that exists in Canadian hockey culture. Due to the history of Canadian hockey, Canadian teams seem to be more susceptible to hiring key positions in management based more on relationships then merit. Pretty much every Canadian team has hired these guys without any sort of track record at being good at the roles they've been hired for (Tambellini/McTavish/Lowe era in Edmonton as well as hiring Pat Quinn and Ken Hitchcock past their best before date , Benning in Vancouver, Bergevin/St. Louis in Montreal, everyone in Toronto).