Doesn't Ayacho have a few years of seniority over Fukumura? C-ute isn't the 'flagship' group, but Maimi got the role because of her seniority.
Don't forget that after Sayu's grad, Cute became senior to MM.
Anyways, the only reason for this discussion is because for some reason, even tho Angerme's major debut was before 9ki joined, MM is still senior atm.
I do hope that Ayacho gets it tho, like you said, she has 4 years of seniority over Fukuhime. The only thing it comes down to now is wich one they will chose over the other, group seniority or member seniority