To be fair, most genres are not needed either. Josei, Isekai, Seinen for example. I would argue that most of the genres except the main ones are unneeded, for the tags can fill that information in. GL and BL can be tagged with the romance genre, for example. And till this day, I still don't even know what's the actual difference between Adult and Smut. Still, I want Xianxia because it's like a unique genre like LitRpg at this point. Don't pretend that isekai and other trashes are not trash. We can look at any genre and pick the trashes to distort the actual view with the genre itself. Isekai also followed the same pattern. Even more fetish-y Gend-bend Girl-Love. 'Reincarnate as' story is also one of the tropes. They are not good or worse than Xianxia— it's just your bias.