My bad. I oversimplified tbh. While some fell to the Portuguese, others prospered with their arrival. The Swahili city-states were never united under one rule.
In the warfare, Portugal had the upper hand for a long time due to the caravel and gunpowder. This changed when the Ottomans allied themselves with the Swahili and supplied them with gunpowder against their common enemy. So there’s nothing wrong with your concept.
As for Kongo and Shona, they fared better, Portuguese gunpowder not being so advantageous on land.
However, I imagine that we will not be able to add all the African civs possible, so I would give the Swahili bonuses to Somalis, since they lived similar situations with Turks and Portuguese and also have more options besides ships and gunpowder. But it’s just my opinion.
I did this summary about the Swahili war if it’s helpful.
This article here explains the Swahili history much better than I do.