R5: Just to prove a point. You can make the AI better without making achievements impossible. I have most of Africa and capped the UK. No need to fight as much in Africa as I did, but I didn't feel like cheesing. Germany declared on me a few months after I dropped into the UK, so I cut it a bit close. Once you got a bit of territory for puppets and manpower, you can ignore Africa.
Because of Belgian Congo, you can't do the final releasable for the actual Crusader King 2 requirements. I might pick it up later and finish the job. Added a screenshot to show, why templates does not fix the issue with the AI.
If you want to give it a go, here is the save: https://disastersavior.com/public/disaster-saves/cede3486-d01e-4afe-a522-7e02c4e700fb/
It's on 1.17.3, because something about Japan declaring made me crash.