Unfortunately, you are. I don’t know that I’ve been to a restaurant in Canada that doesn’t accept Amex.
That is definitely a violation of their merchant agreement. Amex does not allow that. Report them.
I don’t know where you went, but I found several places in Ireland that accept it. I would peg their acceptance rate (based on my own experience) around 65%. Acceptance in the UK is even higher. And I definitely wouldn’t say “many stores in the US won’t take it either.” Acceptance in the US is like 99%. Are you just making up stuff?