I'm not from the US so I'm probably misunderstanding this whole conversation. What's the difference between "a group of people getting together to protest and demand rights" and a union apart from the union being a legal entity?
What you wrote in your edit is what a Union means in Europe, it's just formalized as an entity.
Would you say that a labor party is a union? I wouldn't. A labor party is a labor movement though. If you call labor parties unions and say we should be thankful to them, then I agree, but that is totally different from workplace unions.
What you wrote in your edit is what a Union means in Europe, it's just formalized as an entity.