If it is true that festivals are biased towards male bands it is a shame because I'm sure like most of us here it never enters my mind to listen to one band/act over another based on gender, it's purely based on whether I like them or not.
To be honest female acts/female fronted acts have been out performing the guys for me in the recent past. Off top of my head London Grammar, Lana, Daughter, XX, Haim, Wolf Alice, Billie Eilish, Christine and the queens would all be on my wish list for a festival.
If there's something in the way the music industry, background booking processes that is skewing the balance that's what needs solving.