I agree and I think it’s technically possible for devs. I found a bug that allows it in a very specific case (3rd post of this thread: https://forums.ageofempires.com/t/how-to-build-a-custom-home-city-deck-in-the-scenario-editor-with-a-xml-file/198016/3 )
"In multiplayer when you play a more recent civ than the scenario.
For exemple, play Mexicans on a scenario made before the Mexican update.
I think, there is no default mexican deck saved in the scenario, so the game allows to choose your own deck.
So an option can be created by the devs which removes all default home city saved in the scenario and allows players to choose there own decks."
PS: I added this request in the main post.