For me it’s probably Arabia. They used to be A tier as one of the only ways to go religion on high difficulties but now you can almost always secure one as any civilization and holy sites are some of the best districts. With how important getting holy sites is, ESPECIALLY since Arabia has bonuses towards worship buildings, it’s kind of crazy how they’re incentivized to wait to build them when civs like Byzantium and Russia can get them much faster while still getting faith.

Their other bonuses are pretty lame too. Getting +1 science per converted city is pathetic. Mamluks are a powerful UU but knight rushes are no longer that great unless you’re Byzantium because of walls. Getting universities up early means you have to invest a ton of production just to get them, and all they get is extra faith which is based on adjacency… on a civ with no adjacency bonuses or start bias.

Righteousness of the Faith is a pretty great leader ability but you can’t really carry a civ with one good ability.

I would -give the shitty flanking bonus Saladin a free general after receiving his great prophet, that would help out mamluks quite a bit, they kind of need a general to function well and Arabia is already trying to build campuses and holy sites, so it’s hard to fit an encampment in.

-For the civ ability, buff the science so that it starts at one and increases by .5 per era, so in the medieval age it would be 2 science per turn, industrial 3.

-for the last prophet, let them pick any founder belief they want, this might be a little op but if they need to get the past religion at least let them get decent beliefs. To balance it have them convert all prophet points into faith immediately so there’s a downside.