Still, they appeared with Mario. They are Mario villains.

You're not giving enough credit to the villains. I'm a proud sponsor of the domiance of villains in games. They might lose against the heroes on their own, but together, they can clearly provail.

With Belome possibly eating Mario or Luigi, Giga Bowser marching around and blasting them with Flame Breath, Bowletta doing much the same, not to mention Booster charging with Loco Express, Mario and Luigi aren't the favorites by any measure.

Please don't make another post 98% about Master and Crazy Hand. Fight damn you!!!