I worked on one of the most historically/mythologically-driven games of all time: the classic MMO "Dark Age of Camelot." It featured three realms, one based on Arthurian legend and English history, one based on Norse mythology and Scandinavian history, and one based on Celtic myth and Irish history. It had female playable characters, and it came out over ten years ago. We had plenty of mythological, historical, and literary scholars who played our game, but complaints about female characters ruining the "immersion" or "accuracy" were pretty rare.
One of the reasons I like the MMO genre is that everyone just assumes that there will be male and female playable characters - it's been the industry standard since the genre's inception. And once you start development with that assumption, it really isn't that onerous. As for historical accuracy, well... there actually is a decent amount of information relating to real female armor - some ceremonial, some not. Mostly, it differs from male armor simply by having a few different dimensions - chest to waist to hip ratios being different. That's pretty much how armor was handled in Camelot: identical armor for both genders, with just a bit of tailoring to make it suit different body types.
Evidence suggests that women have been involved in combat (and a lot of other stuff) pretty consistently for most of known history, but a lot of bad research, bias, and deliberate female erasure has occurred.
We Have Always Fought was a good article going around a year ago that explained some of this. Archaeologists keep finding people buried with weapons and assuming the skeletons are male, only to have tests done years later prove they were female. People used to assume cave paintings were mostly done by men, but analysis of the relative hand sizes of the handprint "signatures" that accompany them has recently suggested that these artists were more often female than male. And now that we're starting to see more links between viking women and combat, we're starting to ask the question "why did we think only men did the combat, again?" and the answer is usually "duh, well we just naturally assumed!"
Of course, knights and samurai are easy-to-cherry-pick narrowly-defined class-based roles that were overwhelmingly male. Ok. Give me your top 10 samurai or knight simulators that are all about following the orders given to you by your lord in a world that contains no magic. That's what a "historically accurate" knight or samurai game would look like, if your goal was to capture the most typical experience of someone in that role at the time. If you're already going to go against historical reality enough to give your character personal agency in what was typically a rigidly hierarchical system, then you might as well also explore the edge-cases where women had similar roles, even if they weren't officially designated as samurai or knights. And if you're altering your setting enough to include magic, dragons, demons, time travel, or the undead... well then you've pretty much got no excuse.
Various World/European wars are also interesting to look at because sure, most official military combat roles were for dudes. But if you research people who were running around being awesome spies, resistance fighters, assassins, and intelligence agents, there were a huge number of ladies. That's putting aside people like the
night witches, the Soviet Union's elite force of female bomber pilots. Or the
Soviet lady who bought a tank to kill Nazis with while on a quest to avenge her dead husband. Yeah, the Soviets were waaaaaaaaaay ahead of us at this point, women-in-combat-wise.
What other wars you got? As we've already established, the most famous assassin of the French Revolution was a woman, and for the Napoleonic wars, you've got Juana Galán (tell me you wouldn't enjoy a social links/tower defense town game where you played as a smoking-hot brunette who had godlike combat abilities with a stick, and I will call you a god-damned liar). Fact is, women have always been on the front lines in nominally non-combat roles, and gotten
caught up in actual fighting as a result. Heck, think about it... what better way to show actual combat skill progression than to have your main character be someone untrained who is literally learning to fight as you go?
History is filled with stories of women who have fought, and that's just what's survived several centuries of a historical and literary tradition utterly dominated by white men who just assumed, by default, that anything interesting they discovered was probably done by a white dude, often with basically zero justification. Did you know that
the historical figure more closely analgous to the Lone Ranger was black? You probably didn't, because a few generations of writers have gone around stalwartly whitewashing and gender-erasing portrayals of various historical eras, basically just assuming by default that white guys were the only people who mattered.
If you're putting limitations on your story by picking the narrowest possible social group and saying "Oh, I want my main character to be typical, in everything other than ability level, social mobility, daily life, type of missions they're involved in, and kill count," then you've gotta look deeper at who is creating those limitations. It's not history... it's you.