You make some good points but I am not sure how you arrive at the conclusion that the Canadian hockey pool is half of what it was. You provided good data but this conclusion is a leap.
If Canada peaked at roughly 480,000 births, and had roughly 370,000 and 348,000 when Sid and McDavid were born (respectively), how do you get down to barely half?
Demographics of Canada - Wikipedia
Even now 78-80% of Canadians identify as either Canadian or English or French or Italian or German or Scottish or Irish, and only 22% are minorities. So let's assume precisely 0 minorities are in the hockey talent pool. I mean, that's unfounded, but let's allow for it. That still would reduce the applicable births in 2020 (372,000) by 20% - resulting in 300,000. That's far more than half the peak of 480K.
In 1999-2000 that same figure for people of color figure was 13%:
People of Colour in Canada (Quick Take) | Catalyst
So McDavid's generation goes from 348,000 babies down to roughly 310,000, again, assuming your theory that non-whites don't play hockey is accurate, which it isn't entirely.
Crosby's generation presumably goes down by less. Maybe 11%? So instead of 370,000 it's more like 340,000?
Visible minority - Wikipedia
As for the speculation that you need elite hockey school now vs you didn't way back when, or economic privilege is somehow far less now than ever before when it comes to hockey, I find that to be highly speculative and anecdotal. If a young athlete is supremely talented enough to make the NHL, I'm not convinced they would be completely overlooked now whereas they would be found before. I had several guys in the history forum tell me that today's players can't afford hockey - therefore the generation that grew up in the Great Depression era had a huge advantage (Howe, Richard, Beliveau, Harvey, etc.). Seems rather unlikely to me.
So Sid's generation had a mere 73% of the largest generation (I assume 460K not the peak of 480K because 480 was not sustained) if we assume all non-whites don't count when in fact some of them do?
But even the above conclusion is poorly estimated because it assumes the immigrants of the past were insignificant or they all played hockey. Neither assertion is remotely accurate. Immigration is not a new phenomena in Canada. In fact proportionately speaking, way the hell larger immigration waves happened from 1890-1920 (400,000 in 1912 alone) and 1940-1970 (282,000 immigrants in 1957 alone vs 225,000-275,000 throughout the 80s) than lately. Did those older immigrant populations play hockey? I am not aware of a big influx of Portuguese and Italians into the NHL after WWII. Are you?
After you factor in the older immigration waves, perhaps no adjustments are necessary at all, and the raw birth rates may be the best measuring stick.