As an outsider, I do seem to think that NijiEN was at its peak when it was up to Luxiem. It had the perfect balance of 10 females and 10 males. The males were killing it with their numbers (I think back then Luxiem gets higher CCV than most of HoloEN) and the females weren't doing so bad either. I'm quite sure back then there were people who actually believed that NijiEN were on their way to surpass HoloEN. (I believe at that time HoloEN weren't doing so well)
Kind of agree here, that's when NijiEN really hit their stride, 10 females and 10 males was after Noctyx debuted. I was actually watching a few NijiEN's around that time, however just as I was finally getting comfortable with the new faces from Noctyx, NijiEN debuted another wave, and I just gave up keeping up to date and only started watching occasionally. The issue for me was that they collabed so much around that time that I felt I needed to at least have some awareness of every talent (not watch them all, but see a few clips, read a bit of info, at the least), so ILUNA's debut made me peace out.
Yes.
1: Pomu, Elira, Finana
2: Selen, Rosemi, Petra
3: Nina, Millie, Enna, Reimu
4: Vox, Mysta, Luca, Shu, Ike
5: Yugo, Fulgur, Alban, Sonny, Uki
6: Scarle, Maria, Kyo, Aia, Ren, Aster
7: Doppio, Hex, Meloco, Ver, Kotoka, Zaion
8: Bandage, Vantacrow, Yu Q
9: Kunai, Victoria, Claude