Yeah, I agree about the style/image.
Another option would be let Mayu go solo completely and form a totally new unit with the rest of the (non No Sleeves) Ogi girls: Aika, Harugon, Ayaka, Nonaka, Komori and Matsubara.
One of the downsides is that they won't have a powerhouse member to lead the group and/or boost the sales. 3/6 didn't make top 40 and the most popular one would be Komori iirc. Plus it'll be very hard to shake the WH roots if 4/6 came from WH... So yeah, that probably won't work well either.