Like
..... Waluigi?
I admit I preferred Waluigi simply because to me he'd be another joke character and could sort of represent the spin-offs of the mario franchise: Kart, Tennis, Strikers, Golf, etc. Aside from him though we could take something like Kamek who plays a big role in a few games, I'm personally biased towards Geno as well, and even Paper Mario if you want to have something of a unique character who's more important than her. It's just a really weird inclusion overall and after her being shoehorned into 3D World, we now have her here too.
Of course her being in the sports titles makes sense, it was her inclusion in 3D World that made me feel that way. It was the next Mario platformer, it made no sense for her to appear given that it has nothing to do with the Galaxy games. They're giving a lot of importance to her and I just think it's odd.