X Japan wasn't/isn't Visual Kei.
X Japan was/is Visual Kei.
Now, both of those sentences can be true or false. It all depends on how you define visual kei. Some people define it as what emerged in the 1980s, with X, Loudness, D'erlanger, Color, etc. Some define it as what Malice Mizer and the like started in the 1990s and that X was just visual. As long as we don't clearly define what visual kei is/was, we can't really say anything and all arguments become pointless.