I agree these are helpful paraphrases-- but as a practical matter increasing the burden on the person trying to point out the offense or marginalization isn't necessarily a good idea since it often very difficult for people to call their friends and acquaintances on such matters. For example, I imagine it is very difficult for a black person surrounded by white people to call out behavior that makes them feel marginalized-- there is a great deal of social pressure against this. In normal social contexts a minority should be free to express how something makes them feel without being expected to enter into an extended defense of the matter.

Here at Less Wrong, I almost always translate "is x-ist" in the way you suggest and think it is worthwhile where the goal of the discussion is truth seeking (I'm not a member of many relevant minorities, though)