I agree that renumbering routes would involve some difficulties, but it's been done before in numerous locations and eventually everyone adapts. If they had renumbered every segment of the main route of the TCH to 1 or some other number when the route was first designated, then today nobody (except maybe us) would remember that so-and-so was originally route 1 but it was forced to change numbers decades ago because of the TCH. But my main point wasn't that provinces should be forced to apply route 1 to the TCH, it was simply the philosophical statement that it would be better if the route had a consistent number across provinces and my curiosity as to why that wasn't the case.
Put another way, what would've been better in the Interstate and US Route systems in the States: that roadways change numbers crossing state lines, or that routes keep their numbers across those state lines? Obviously, it's better and easier for following those routes that they maintain consistent numbers. But it would've still worked if we'd kept the named highway trails and cosigned those with the routes; it's just that the Interstate and US Routes as they are constitute a more efficient way to indicate a multi-state route than, say, the Lincoln Highway consisting of multiple differently-numbered routes.
On another note, I don't necessarily even think 1 should've been the number for the TCH. Other numbers, like 0 or 100, would have been interesting choices, and not because they'd represent extensions of US numbering schemes, but more for them being unique, distinctive numbers.