Okay, except that the word "history" is nothing to do with male or female, so "herstory" is a meaningless word, from that standpoint; it's far more accurate to say "women's history".

The etymology of the word "history" is quite unrelated to gender. It's derived from the Ancient Greek ἱστορία (historía), meaning "inquiry", "knowledge from inquiry", or "judge". It isn't even tangentially related to gender: the root "histor" has been mistranslated as "wise man", where in fact it means "knowledgeable" or "expert".

"His" is from roots in Old English. "Her" is from the Middle English, also going back to Old English roots. It's an accident of the evolution of the English language that the word "history" and these possessive nouns are even in the same room with one another.

I'm a feminist, but I'm an historian as well. Both are equally important; just as the words we use are important.