Interesting to read your perspective, TB. I agree with more or less all you say when talking about late spring/summer/early autumn fishing, with water temperatures above about 45F.
But my impression is that your salmon fishing is mostly conducted in such relatively warm water conditions, which isn't the case over here. As I understand it, your season is much shorter than ours. Over here there are rivers in Ireland where the season starts (and fresh fish are caught) on January 1st. There are also rivers in SW England where the season continues, and fresh fish are still caught, well into December. The River Tweed has perhaps the longest season of any single river, opening on Feb 1 and closing on Nov 30.
I suspect, therefore, that we do more fishing in cold water conditions than you. And this is also true in Norway and Russia, where you will encounter what we would regard as 'early spring' conditions in June. It's not all that uncommon in the early part of the season to be fishing in water that is only a few degrees above freezing. In these conditions salmon, like all 'cold blooded' creatures are much more sluggish and there is definitely a need to present your fly slowly and close to the bottom.
I think that the development of fly lines over the last 20 years has changed things a lot. Back then the 'Wetcel 2', with a typical sink rate of a little over 3ips, was regarded as a fast sinking line. And in the high cold water of early spring and late autumn this alone is simply not enough to get down to the fish in many pools. On the lower Tweed in November, for example, people occasionally resorted to 'leadhead' flies which were a brass tube with a drilled .22 bullet fixed to the front. Horrible to cast, and in unscrupulous hands a tool for deliberate foul-hooking, but they did certainly have a legitimate use in high water conditions in certain pools.
With modern fast-sinking lines this sort of heavily weighted fly is now much less necessary. I believe the swimming action of a light fly on a heavy line is much better, whereas a heavy fly can appear lifeless in the water. A heavy fly also increases the risk of getting stuck on the bottom, whereas with a light fly and short leader the line can touch the bottom and the fly will swim a few inches higher. So I would always rather fish a heavy line and light fly than resort to a heavily weighted fly. But there are times and places where weight is still a necessary evil.
I would be interested to know the duration of your season in Canada, and what you would regard as typical water temperatures in that period.