The conditions of WW1 were so horrific that it is a wonder that they were not all rendered "insane". Vietnam was also difficult as it was the first occasion of regular troops fighting guerrillas who weren't bound by the same rules of war.

WW11 was not much esker, but again, the returning soldiers were treated as heroes and offered education, housing and so on. As well, there were a lot more of them and there is psychological strength in having many comrades with whom to talk.

I have never personally seen any writings comparing the actual rates of what we now call PTSD in soldiers returning from the various wars. I doubt that numbers were actually kept in the past. We will likely never know.

As for your first paragraph, I live in Quebec and therefore never hear a peep about vets here. Thanks for the view in the rest of the country.