>>9907853It is though. You're underestimating how much the hardcore otaku audience hates anything even resembling gyaru, nevermind actual dark skinned characters. Hentai is also a poor metric to judge by because you're entering a niche market within a niche market. Even then, I wouldn't think they would outsell content with lighter skinned characters.
It has almost nothing to do with her design, same with Flare. FGO released a dark skinned/gyaru BB for one of their summer events and the otakus sperged out over it so much that they had to add a light skinned alt costume. Literally the same design, just the skin color changed. I won't even get into their overreaction and hate of Scherazade.
Between racist weebs and hardcore otaku, the sub gap just about makes sense.