The idea that a desire for increased historicity would be a roadblock to removing or altering the virtue is pretty bizarre, not only because (as folks have pointed out) this is a setting that by its nature takes liberties with historicity or because people have different ways to enjoy Ars, but because the current Flaw being applied in any sort of general sense to Mythic Europe is itself ahistorical. Granted, my familiarity lies mostly with cultures and histories that exist on the geographic edges of the Order - al-Andalus, the Levant, and Muslim Anatolia - but just the existence of differences kinda negates the use of the "not historical" argument for universally punishing gender nonconforming people. There are tons of examples from history and period culture - one is the openly masculine coded and garbed warrior women of the Türkmen frontier epics of Western Anatolia (who were decidedly not "regarded as [freaks]" even in a deeply patriarchal medieval culture.) The epic hero Kan Turali rejects the conventionally feminine marriage partners offered as being not to his taste and goes searching for a warrior woman - explicitly called a "man-woman" later in the epic.
'You don't want a girl; you want a dare-devil hero to look after you, and [together] you can eat and drink and be merry.' 'That is so, my dear father,' he replied, 'but you'll go and get me some pretty dressed-up doll of a Turcoman girl, whose belly will split if I should suddenly lean over and fall on her.' 'Son,' said Kanli Koja, 'finding the girl is up to you; I'll see that you're fed and provided for.'
The girl he finds, Saljan the 'man-woman', is certainly not ostracized - she's a princess of Trebizond (Theban Tribunal represent). There's a lot of high adventure before they run off together but another relevant part comes in when Kan first spies his bride to be armed and armored; he's so moved by the sight that he makes prayerful sujud right on the spot.
Kan Turali opened his eyes, he raised his eyelids and saw his bride on horse-back, dressed for battle, spear in hand. He kissed the ground and said, 'I hold the faith and I believe; my wish has been granted in the court of God Most High.'
It's not an isolated case either. Nomad noble Banu Chichek gleefully wrestles her beloved Beyrek, who is impressed and sort of scared by her "warrior strength". The daughter of the Caesar in the Battalname slaughters an army alongside the eponymous hero. Just over the border in Byzantium, there's the Epic of Digenes Akritas - the half-Arab, half-Greek frontiersman whose exploits strongly parallel those of his Türkmen counterparts - that features the ambiguously masculine raider lord Maximo. These legends are in currency depending on area of Mythic Europe, particularly among the Oghuz peoples in the Transylvania and Theban Tribunals and their neighbors, and someone wanting to build a character around them would definitely be let down by the Flaw as is.
It's also not just myth. al-Andalus is full of situations concerning ambiguous gender, from beauty ideals favoring what could be called androgenous markers to the liminal spaces occupied by eunuchs to concubines and courtesans who dressed like men habitually. A useful discussion of Persian gender norms and their fluid nature before modernity can be found Najmabadi's Women with Mustaches, Men Without Beards which tbf is focused on the early modern and the end of amrad sexuality with the introduction of Victorian norms to Iran but certainly explains the existing culture well. Hell, we have examples of literal legal gender changes from this period (the Mamluk age is a little after the conventional start but certainly is in full force before the close of the 13th century) in areas covered in 5e game books:
...In the early Mamluk period the transformation of girls into boys is a cause for public celebrations...there are later cases in which courts are asked to confirm a female sexual identity for persons who, by all outer appearances, were physically male.
The citation for the above being Tamer el-Leithy's “Of Bodies Chang’d to Various Forms . . . : Hermaphrodites and Transsexuals in Mamluk Society” (apologies for language)
Realize now I may have rambled a bit but yea I just don't understand the historicity angle, which anyways is not good enough as an argument even if it was correct. Sure there are many cultures represented in Ars books that hew closer to the way the Flaw as is understands the question, even a majority of them probably, but then there's an even stronger case behind using some of the more flexible fixes listed above that allow characters to be tailored to the culture they are from and the experience they want out of the game. "But history" - as it usually is in these sorts of arguments - is more about myopia, limited research, and a simple unwillingness to listen to other (often minority) voices.