Sure it’s still _difficult_, but no more difficult than any other historical definitions at the same level. And remember that Western civilization doesn’t have to be unique in every way, in order to talk about it as a separate thing. You and I probably have characteristics in common. We’re still separate individuals. Tying the definition to historical specifics in the same way makes it perfectly reasonable to talk about Western civilization.

I any case, I don’t think it makes sense to talk about “western civilization” as if it is one thing, it is in my opinion not even resembling a clear and stable object. There are of course some interesting ideas or ideals that great thinkers have tried to distill, for instance in the US constitution or the UN declaration of human rights. But it is in know way obvious that these are specifically western, and they are for sure not representative of western political or social history.