Those gatekeepers would be wrong.
Take Age of Empires 1 for example. I think it’s 100% ok to add the Olmec Civilization into the game, the most important earliest known Mesoamerican Civilization-Empire to exist. Just because they never contacted any other civilization inside the current game, doesn’t mean they didn’t exist during the same time period.
I hate it that we need this “For a civ to exist it needs to be connected in the timeline somehow, even indirectly. For example, Civ A only had contact with Civ B, but Civ B had contact with Civs C through H therefore Civ A can exist in this game”.
That’s stupid. My philosophy is “if it exists during the timeline, even unconnected, then it should exist in the game”. We don’t need to touch the Early Renaissance period, outside of the Middle Ages like Age 2 did, to justify putting Aztecs into the game. Just put the Aztecs into the game, we don’t need conquistadors.