You know? After seeing another piece of fanart today I think I just assimilated the headcannon that Hilda is rather flat chested but compensates that with her great game of thighs, hips and behind, while Rosa packs massive dobonkie donkie honkies but is kinda flat from the waist down.
Just imagine them being competitive because of that instead of them just being rivals because they both think they are the best of the two.

Respect the booty.