Just give the fella fellas the right to wear bodysuits if we want to flatten playing fields. Have the guys make the concession for a change.
Although to be honest, as you said, even that's probably unnecessary, as hormone/hydrodynamic modifications will confer more disadvantages than the advantages the suit will grant.
I suppose you might need to cover the edge case of transwomen swimmers who do LITERALLY nothing near sticking on a bit of lippy. We can't gatekeep trans after all.