What about Non then? Her spongey soft butt's Reflection capability may only work with the efficiency it does if the mass of her tush is contained in a regular swimsuit.

The other obvious reason against thong bottoms for all is the risk of flashing their bits.

Miyata and some of the other girls have prior training. Miyata is a judoka, Nozomi is a gymnast. They're not going to have to train as hard to get up to that peak level of fitness because they were already there.
Many of the others just have curvy bodies or are musclebound.

You're thinking too hard about this Buff.