Yes, that's very apparent that this happens with new models, even for similar characters, because you're better off modeling new characters with different facial features, build, and hair from scratch than editing them (you will mess up UVs if you rely only on texture edits and vertex edits to get what you want). Even characters like Baby Luigi have unique UV maps. I just said that "She even looks like her head was Frakenstein'ed onto Peach's body.", which means that part of the post wasn't meant to be taken literally.
She's still a low-effort character to make, however. Modelers make tons of models per week, and modeling a character with a similar physique to another character won't take more than a day to fully get down if you're a professional. The animations take the most time to make because you practically need to keyframe a bunch of animations and as you said, Peach already has. And practically all of her moveset properties are from Peach, meaning they pretty much don't need to tweak anything if at all when it comes to bug and balance testing, which is another time-consuming part of the character process.
In addition, particle effect animations aren't all that hard to tweak.
