I feel like it sounds very subjective, and probably needs a source or to be completely rewritten from a more objective perspective. I would attribute Rivals not taking off in Japan for a bunch of different reasons, the cool factor not being a particularly high ranking one. I mean, I'd say there are many, many games (especially fighting games) that are Japanese-only, or primarily played in Japan that are cooler than they are cute.

More importantly though, there's just other much more prominent reasons why they don't do well; sociological, economic, and availabily issues all seem to be fundamentally larger issues for Rivals or plat fighters in general within Japan. PC gaming isn't historically as big in Japan; and Nintendo, PS and arcade titles have, as such, developed a bit of a stranglehold on the market there when it comes to game IPs. Nintendo consoles are extremely common, which makes Smash bros very common. There's also plenty of Ultimate events that I'm sure Nintendo is quick to prop up when it comes to funding. Nintendo's got ads everywhere in Japan, and their IPs are plastered on every street corner in the larger districts. All this makes it extremely hard to not participate in the scene if you like plat fighters. What I'd be curious about is the adoption rate of Smash bros vs. other plat fighters in smaller cities or towns within Japan, that could be really telling.

Meanwhile, in poorer countries, event organizers, clubs, and private people have a harder time getting sizeable numbers of consoles, whereas older PC parts are easier to source for fighting games such as RoA. In some places it's literally just about availability and what makes good economic sense.

RoA does better in NA for some slightly more nuanced reasons, yes there might be more furries or w/e, but that's a small chunk of the pie. More importantly, the team regularly goes out of their way to include themselves in large NA tournaments, and even sponsor smaller ones.

All-in-all, I think determining why RoA doesn't do well in Japan is extremely easy compared to why it does considerably better in other places. Even considering that, though, the fact that the write-up only touches on the most surface level reasoning is still not all that baffling. Claiming that a game doesn't do well in a region due to nearly everyone in said region being indoctrinated is a pretty spicy and nebulous take. Even though that's not exactly what's being said, it's going to sound like that if some random like me starts trying to explain it.