I've figured out why Rolstoppable doesn't like the Smash Bros. franchise.

[wfz]

Mario Kart has just as much "Nintendo" in it as SSBB, so that can't be the reason. Your other reason holds up well enough though.

I think the reason Rol hates SSBB so much is because sonic has an extremely lame and unoriginal move-set, it's like they didn't even try to make him cool.