I mostly play the game in singleplayer, therefore i have quite a bit of feedback about the bots...
-Japanese are broken. They start normally but after a few minutes they idle their villagers and dont progress at all, making them an easy target.
-the Germans seem to have the same issue, to some extent. They progress quite normally, but slower than they're supposed to. After Mid-end game they had only a few buildings and they werent producing much units. Not much competition..
-Bulgarians had the same problem as the Japanese. They made a few villagers, harvested ressources, buil a building or two and then spent the rest of the game harvesting ressources and exploring the map..
-There was a few more civs that were broken, but i dont remember. Ill try to keep this list up to date.
I think i was playing on the second or middle difficulty. I know the first one is completelly borked...