You must be unfamiliar with the clothing women usually wear when praying. Its large, draping and for a pervert there is nothing to see.
If the concern really was men looking, Muhammad could have easily mandated women wear clothing that is appropriate for going for the sujood and rukhu instead of completely banning women becoming Imams for or being in mixed gender prayer.
Another simple solution is to have a screen upto the female imam’s hips for when she bows down and prostrates, if we insist on the jamaah not having mixed gender.