Egyptian mythology is interesting, but there are many overlaps with the Academy. Perhaps it would be worth adding Celts, Mongols, and Nanais! Let's release our own game, Heroes of Might and Civilization VIII.
Added 1 minute ago
I've always considered the Sylvan faction to be Celts, but there's a lot mixed in.
But personally, I think that simply focusing on a specific culture is not a good idea; you need to start from the world, so that the faction looks harmonious.
Added 1 minute ago
And regarding the overlaps, well, half of the factions have dragons