In civ5 AI was already barely capable of posing a danger to a human player and barely capable of mass conquests, often still losing many units to terrible sieges. But logistics of this game were also really frustrating me as a human - moving units through rough terrain was incredibly tedious and problematic. My worst nightmare in this game was AI founding cities in places like "mountain, river, mountain, jungles, river, swamps, bottleneck, coast" (hills in the 1st ring around the city, plains in the 2nd ring, to ensure you can't shoot at it from afar), which was like 30% of all cities anyway. Two thirds of my frustration in this game were insane siege minigames like this. On the plus side, this design ironically added a lot of challenge to warfare. Then imagine devs sitting and designing civ6 and one of them saying: 'You know what? I want cities to become way more resistant and movement rules even more horribly painful. Also, some cities will also have a second city center (camp) shooting too. I bet AI will be able to deal with that.'