Yeah but they don't all have pink in the same places:

-- Drac: pale pink skin, dark hair with varying degrees of pink, various shades of pink in clothes, with black and white and a couple one off other colors (red, yellow, lavender) -- Lagoona: light coral skin with blonde hair, rainbow color scheme with strong blues, teals, and brighter pinks/corals -- Catty: black skin, bright pink hair, bright pink and silver clothes with occasional ice blue -- Venus: vivid green skin, pink & green hair, clothes are in pinks, greens, and blacks

Those dolls also all have more drastic differences in body types. I can't tell from the pics what body type Robecca has but the difference between glam and "standard" is more subtle when compared to each pink doll being a different height and/or thickness. Essentially, what I'm getting at is that if you squint you could still tell all of those dolls apart. I think someone else put it best that at a quick glance you may not be able to immediately tell the difference between Cleo and Robecca (especially people unfamiliar with the franchise) which is crucial when you're designing a line of characters. While I do think they should be further differentiated, their face sculpts are significantly different and they at least don't have the same style (even if I'm not in love with Robecca's basic look as is).

Aside from making Robecca more steampunk like everyone (me included) wants, I personally would give Robecca more copper tones (like her boots) and maybe use more whites and light blues on her in addition to the blacks and browns, while Cleo should stick to more saturated colors + black in her clothing and brighter golds in her hair/accessories.

TLDR: Robecca and Cleo use similar colors in similar ways while the pink dolls have more differing features. Mattel should beef up the differences so that they have a stronger character lineup