OK, so there's a few things I think would make the civ-series games a little better
1. Not all the civs start at the same time, as new ones can form as the game goes on
---- City-states band together to become a new civ, but despite their late start, are actually a little more powerful at the outset b/c there are multiple cities when they first become a "new civ"
---- Barbarians that capture settlers / workers have a chance of converting their camps to found new city-states
2. Diplomacy
---- There's too few options for 'trading'
---- shouldn't be limited on the numbers of diplomats you can send to other civs, although maybe you need a certain tech to trigger that one
3. Scouts
--- Why do scouts only level up by getting into fights? What does combat have to do with being a better observer?
4. Wonders
---- Civ 6 fixes this a bit, but there's waaaaaaay too many wonders allowed in any one city
What else would you fix?