Hi!
I decided to try out Ethiopia - phew, that's a rough start! Very difficult, you more or less have to choose if you wan't a city to grow, but not produce anything, or produce a little but with zero growth. The low-quality plains & hills hurt a lot. This is as it should be, I guess, and I've been able to manage through a mix of sucking-up and aggression.
However, there is one problem - settlers. The settlers are expensive (and they need to be to slow down the europeans), but it has bad results for africa, since the africans aren't capable of producing enough settlers. The entire western part of africa was settled by Spain, Portugal and Rome.
Arabs & Persians settling parts of eastern africa is ok and historical, but a "White Nigeria" has to be stopped!

I ended up rush-buying settlers (at ca 600 gold each!) rather than waiting 40 turns for them to finish!
One solution would be to add a western african civ, but I know you wan't to avoid this, since they don't have a leaderhead and it would requiore removing some other civ, and I respect that. But how about reducing the cost of settlers for the Zulus, Ethiopeans and perhaps Egyptians (they have a lot of food, but no production). Central asia has a similar problem, colonised by european powers between 0AD and 1000AD, so maybe the mongols need this to...
An alternative would be to disable them to build medieval & Modern settlers, so they can keep building cheap Ancient settlers? Or give them cheaper early settlers, but keep the upgrade to expensive Medieval settlers? I can test this Rhye, if you are intrested.