No, no, I see FBM's point. Baby Mario and Baby Luigi can't really be treated the same as Wario and Waluigi (or just Wario, at least) because they haven't broken off into a spinoff series for themselves, whereas Wario's primarily moved on from the Mario series into not one, but two series of his own, except he still participates in spinoffs. I'd love to be proven wrong, but I don't see it happening.
Though, to be honest, the Mario vs DK games might damage the point slightly.