The point was that you weren't explaining it, at least not thoroughly enough for me to understand you. Now that you are, we can talk. (You can explain the "confusing actual play styles/mechanics with plot points" part at your convenience.)
SPM may be more platformer than RPG, but it's still primarily a Paper Mario game. It's sort of like how Yoshi's Island is the sequel to Super Mario World in America which is the sequel to Super Mario Bros. 3 in Japan. Even though its connections to SMB3 are spotty, it's more like SMB3 than like Yoshi's Cookie, even though Yoshi's Cookie is in the same series. Rubix that analogy around a bit and it should be kind of similar.
If, in the future, we get both a SPM2 and a more traditional PM3, then I'd be willing to consider SPM its own genre, or possibly part of the 2D platformer series, but until then, for our purposes, it's a Paper Mario game, meaning it's a Mario RPG, even if, measured in absolute, Mario-neutral terms, it's more like a platformer than an RPG, and that was a long sentence.