they're called radical feminists
they're still feminists
their views are radical, hence the radical modifier
but they're still called feminists. It may not fit the dictionary definition, but they're still called feminists almost everywhere, just with the radical modifier placed on it. People don't always use the dictionary definition of a word, and really, why would you care whether or not they're categorized under a particular term? It's really pointless. Just point out that an individual is not, in fact, fighting towards equality but female supremacy and literally everything they say is immediately discredited. Fight individuals and ideas, not groups of people loosely held together by a flimsy definition that many people ignore.
The fact Derontchi is trying to call out the entire movement out on being female supremecists is also ridiculous, because clearly it's not the entire thing. It's the whole vocal minority silent majority thing all over again, because I'm willing to bet the vast majority of people you ask on the street "Are you for women having equal rights to men?" would answer yes. That, by definition, makes them a feminist.