5 factions is good. To hell with all this "diversity" and dozens of castles. The fewer factions, the more distinct they will be from each other (not only in appearance and content, but also in tactics, play style, etc.), and the better the balance will be. Heroes doesn't need just 3 cities, but 5-6 is probably just right. Besides, if the game sells well, they will definitely make expansions with new factions, so there's no need to worry about that.
According to the timeline mentioned earlier, the Falcon Empire should still exist at that time, right? But based on the articles and the symbolism of the humans in the screenshots, it can be concluded that it's not the Falcon Empire at all, but rather the Griffin Empire. This means there's a chance that the old timeline is completely or partially wrong.
upd
Although, no, it seems I was wrong about the symbolism. Here's a screenshot.