From the ~ 3years I was active as a player/viewer, just to name a few big (over)powered civs/units:
- malay with harbors pre nerf on certain hybrid maps (I didnt play with them right after release, at wich times they apperently had insane stats, but even now they are still very strong, in DE the harbor seems more balanced)
- burmese pre arambai nerf
- italians as a very strong civ on both water & land maps, pre condo nerf (teammates also benefitting from the condotiero)
- Slavs on HD balance (before their farming bonus got nerfed several times)
- Elite battle elephants pre nerf (increased elite upgarde upgrade cost, increased damage taken from halbs) especially broken on WK where trample damage was doing a lot more damage than intended
- AOC mangudai & mamelukes
- malay with harbors pre nerf on certain hybrid maps (I didnt play with them right after release, at wich times they apperently had insane stats, but even now they are still very strong, in DE the harbor seems more balanced)
- burmese pre arambai nerf
- italians as a very strong civ on both water & land maps, pre condo nerf (teammates also benefitting from the condotiero)
- Slavs on HD balance (before their farming bonus got nerfed several times)
- Elite battle elephants pre nerf (increased elite upgarde upgrade cost, increased damage taken from halbs) especially broken on WK where trample damage was doing a lot more damage than intended
- AOC mangudai & mamelukes