Thanks for the overview, you are right that their naval bonuses could still be lacking when compared to top tier naval civs. So far, what helps them in water maps, is the fishing gold trickle, the free Mtepe, and wood savings on Market and blacksmith. I could draft a 5th civ bonus relating to it. Any suggestions?
About the Vikings, they are exceptional in land and water due to free wheelbarrow. It’s just nuts and one of the best eco bonuses in the game. The Swahili on the other hand are historically coast dwellers and truly dependent on trade wealth to source grain and timber from inland Bantu peoples. So it’s intentional for them to be kinda bad in land maps, however, the 20% more resources is not weak since it is similar to Saracens Market bonus that allows them to have absurd Castle Age timings. On top of that they get wood savings and diverse military options. Vikings surely are still better than them in 1v1 Arabia, but in team games the Swahilis are a much better pick, so that is the tradeoff.