Fate has some pretty severe inaccuracies, though most of them are intentional either to make them fit into the Nasuverse better or just because the author felt it made for a better story. Leaving the gender-swap stuff aside, Attila the Hun is actually an alien, Karna and Arjuna have their characters basically swapped (which has a ripple effect on everyone in their story), the Greek gods were robots, the Mayan gods were space fungus, and a bunch of other stuff besides. Most of it gets explained or addressed in the story, but it's still there. Except the Karna and Arjuna thing, that part is because they exaggerated the "noble villain vs flawed hero" dynamic the OG's had to the point Karna is now the good guy and Arjuna the bad guy. It's stupid and drags down every Fate story involving their myth. And I will rant about it forever