I really hope the devs read this thread. [...]
Thank you for putting some serious thought into this. It is an unbalanced area of the map to play. Although the interesting thing is that in the time since I started this thread, I have been publishing my Abyssinian AAR and occasionally folks will respond with their winning Ethiopian strategy. There seems to be three main strategies that you can take to have a prayer of a chance:
1. Alliance by marriage. The Abyssinian king starts out with an unmarried son, and you can get breathing space from the infidels by causing them to hesitate to invade when you establish an alliance with the HRE. I tried this in my AAR and the emperor said no dice, but at least one person has been more capable than I and managed this.
2. Swearing fealty to HRE or Byzantine Empire or to the infidels. Any one of these will get you in the clear, although you may well have to take a huge piety and/or prestige hit to make yourself acceptable (converting from Orthodox heretic to Orthodox costs 500 piety, for example).
3. Assassinating the Shia Caliphs like a madman. Their succession laws make them ripe for civil war, and when they are fighting themselves they are not fighting Ethiopians.
Someone had the good idea (as Axum) of swearing fealty to Abyssinia. This consolidated two Ethiopians realms into a more powerful one.
All this being said, while it is possible to survive as Ethiopian, it really shouldn't be *this* hard. The best ideas to help them, from posters in this thread, would probably be adding mercs they can employ and preventing Holy Wars between Ethiopians and Muslims.