The Suzy/Miss A situation wasn't just Suzy being the most popular member. Suzy was heavily pushed outside of the group and had tons of solo cfs and was in hit dramas and variety show appearances. Miss A also didn't actually promote together that often compared to other groups.
They also had 2 Chinese members whom the gp didn't necessarily warm up to and while Min was heavily pushed in the beginning and stood out at certain times with her Kkap dance, she was too far behind Suzy who was literally promoted everywhere at a certain point.
In nmixx, so far it's just like any other group with one member getting a lot of attention. The other members may stand out more with coming comebacks. The only was I see it getting as bad as Miss A is if sullyoon does a bunch of solo promo at this point. Right now I think the worst it will get to is a Wonyoung situation which isn't even that bad.
I think they'll likely go the aoa route where the visual gets a bunch of attention (Seolhyun) while other members like Choa and Jimin get recognised for their talents and don't fall too far behind.