Why did I ignore such a fun game mode? Because I didn't just start playing the game completely blind, but watched a bunch of YouTube videos about the game first. The problem with that is that people tend to make content about video games when the game is new and shiny. And the empire mode was only added to the game more than a year after release, simultaneously with the third and last DLC, but for free. So the videos I watched were mostly from a time where empire mode didn't exist, which led to me just ignoring the option on the main menu. My mistake!

Empire mode does have some restrictions over planet mode, you can't change some of the settings. But while a win in planet mode just means you have to start a new game, in empire mode you gain some advantages that you can take with you into the next game. Also in empire mode there are added modifications, sometimes even new victory conditions, for a greater variety. So I would recommend maybe playing one or two planets in planet mode when you learn the game, but then switching to empire mode much earlier than I did.