First off, I didn't call it a different "sport". I called it a different "discipline". There's a big difference and if you want to get pedantic, then make sure you quote me right. Rhythmic Gymnastics as practiced in the Olympics and that has kept up to "international standards" are the ones people think about - with a specific set of apparatuses and no tumbling runs. The videos of the Japanese-style mens gymnastics that I did watch, and in my original post I said I watched, show men doing tumbling passes and more moves with saltos and multi-saltos. You casually say "just add tumbling and it'll be the same", but that's just it. They don't have it and it's not so simple to "start including tumbling". I bet many RG aficionados and officials who are more traditional would argue against it with everything that they have because they believe in the distinctiveness of that discipline.
I think that in of itself makes it different enough to call it a different discipline the way pairs skating is a different discipline from ice dance despite so many shared qualities. The way trampoline and tumbling are separated from mens and women's gymnastics.
Me and you can have our differences in opinion, but I do think there can be room for both the rhythmic gymnastics as currently practiced in the Olympics and the more acrobatic style as practiced in Japan that is spreading around. The Spanish mens rhythmic as in the few videos I've seen, seem much more closely aligned to the RG that is currently practiced in the Olympics. The men there seem to want to participate in the sport that is already in the Olympics while the Japanese style diverged into a different entity with shared aspects and even shared apparatuses but with enough different skills and moves and emphasis on those moves in the scoring to argue that it it has different "values" to be its own discipline of gymnastics.
Anyway, you don't want any of it at the Olympics anyway, and none of us have any control over anything, so we'll see what happens. I am afraid that in their journey to seek Olympic accreditation, the Japanese style of RG may start getting corrupted by the FIG but maybe they already have their own issues.