The first campaigns in aoe4 don’t really have any replay value. They should be more of a story like lord of the rings movies, game of thrones or Vikings where it builds up to a epic final battle with 1000s of units fighting.
With the replay value part it could be like your building your own army along the way, making choices, upgrades, units. If you don’t have any choices in the campaigns there’s no replay value.
Or have a conquest mode, but there’s no point in making one if its not better than other strategy games