If it were the Father suing for custody, the mother would hold all the cards. Funny how that no longer applies now that a Lesbian partner is the one suing.
This is no longer true. I know of plenty of cases where the male judge, with an ax to grind as a backlash reaction to the situation that traditionally favors women, has granted custody to unfit fathers and taken kids away from excellent mothers. This is particularly a problem when the father has greater financial resources than the mother.
In many places, the legal decisions have little to do with the best interest of the child and a LOT to do with who can afford the most “justice.”