I don’t play treaty, but in supremacy games I’ve played that dragged on long enough to get everything maxed out they come across as extremely strong.
There are so many things for Ethiopia that are really hard to take advantage of in the short term, but become OP in the long term. Cow Loans has a huge upfront cost, but is really good over time (you even keep Big Benny with it). Loyal Warriors comes really late, but gives huge discounts. Fields take a tremendous amount of time to set up but have lots of upgrades.
There are a few things that combine together to make them really powerful.
Maxed out cows and goats give a ton of influence and can also be periodically sold.
Ethiopia has a lot of food gathering cards for fields.
Most of their units are above average
Italian Firearms makes your cannons above average once you can actually afford them
15% discounted natives and 30% discounted mercs (and they shadow tech)
Reliable good techs and native units from alliances
You can max abuns as soon as you age up whether you use Habesha or not, just build a Monastery in age 1 transition and mine it with a ton of vills.
They do have a donkey and are classified as “cavalry” just like Spanish Missionaries. Definitely a decent meatshield because they don’t cost pop and are pretty cheap.
Their gather rates on Fields after all their upgrades and cards comes in lower for Food and quite a bit lower for Coin compared to the European civs that have all the upgrade cards for Mills and Estates, but I suppose if you consider the effective resource income that Influence contributes, then they should end up with at around the same total resource income. The problem I have often encountered is that, in Imperial, you can’t actually do all that much with the amount of Influence you get. It just never feels enough. By that point, mercs fall behind standard units in the value you get per pop regardless of their lower cos and the rate at which Influence is generated doesn’t really allow for sustained artillery production. Apart from the Cannoneers, the natives just feel too limited in number to make any meaningful difference. Most likely I just don’t use all their various little contributors efficiently enough to get to the point where their combined effects make the civ as powerful as some people see it. I love it for that, though. It feels like you are always cobbling together something in the absence of a one-size-fits-all strategy to fall back on like Redcoats, Ruyters, or Cuirassiers.
I’m not sure if either Cartridge Currency or Solomonic Dynasty make any significant impact even in very long games. You gain 3% of a unit’s total cost in Coin with the former and 1.5% in Influence with the latter. This means if you kill 50 Musketeers you get . . . 225 resources. That’s enough to train almost two Javelin Riders. The Habesha tech granting an HP aura to Mountain Monasteries will certainly make a noticeable difference, but, as the OP mentioned in his opening post, you have to sacrifice one of the much better Alliances to get to that tech. I can’t see either of these factors making Ethiopia OP in treaty games.
I would love for Hausa to have access to Zenata riders, they are very good anti-cavalry. I thought about proposing this, but remembered it had already been done somewhere.
I would also like the university to generate more experience when it is close to the mosque. It should count as an important building.