I don't know, Byzantium has been carving up the Abbassids in my 2.2.0.1 old gods start. Aleppo has just been taken and the abbassids are finally starting to rack up some decadence from their losses, and they lost Antioch to other muslims(can't tell if a vassal declared independance or something else, i'm norman all the way in europe so i only check periodically out of curiosity.). I'll need to keep playing to see if they eventually collapse, but while i don't think they're OP, they certainly seem to be more stable than they should be.
On the flip side, byzantium has been having rebellions almost constantly. Which is surprising that the Emperor has managed to pull off territorial gains. This is with a Viceroy-free Byzantium too since i don't have the CM DLC yet, which means none of the AI can use VR either. AI has done good by byzantium in my current playthrough