Kongo is super late game, the problem is not evaluating the bonuses per se but how the meta is right now, at that point of the game if you can spam culture you win either way and you dont care anymore of production, why would you need production and food when you going for culture? Its a great bonus out of contest but for the meta and the victory condition is not that great.
And same for forest and building kongo residences on there, its too late game, forest is good for other stuff in game pace, you chop, you build lumber mill, keeping indefinitely them there for eventually some more citizen isnt the meta, it does indeed get super great but in a way it doesnt matter.
Kongo has very little sinergy with its bonus if you combine them and how the game is played, while every single bonus is great.
So Kongo is good, but definitely not even remotely top tier.
Why super late game bonus?
Forest/Jungle Bias comes as early as you click Start game
Kongo Neighborhood is Medieval era, like feudalism and industrial district. The snowball you get when you start to build the neighborhood earlier is amazing.
Your UU comes at just the right time to make you survive those horseman rush, not a late game bonus.
Double merchant points kicks in with Comercial district and you build a LOT of those, making the 200% GPP even better.
You start with 5 GW slots while other civs only have 1, this alone is huge in the early game to use those artistic GP that are almost always useless for other civs, if you played any civ with bonus GPP for artist/writer/musician (kongo gets 200% on those) you know the GW slots is a pretty hard cap for these GP and how much +4 culture or +4 faith is in the early game.
The only mid to late game ability is Archeologist for theming artifacts, but you can do fine without them earlier by using relics from some martyr apostles (you get one extra apostle each time you build a theater district / neighborhood) or sculptures from Great Artists. The bonus for theming museum is just insanely good.
I'm actually playing my first Kongo game now. I think it's fair to say their bonuses are geared to lategame – I'm still focused on settlers, builders, and military units at t120. On a tighter map, they might be more useful to me, but on the current game, I've still got tons of excellent turf to settle, so it's hard to will myself into bonuses that aren't as great as having more cities.
I built a few commercial districts but somehow Rome still beat me to a choice Great Merchant. Next one in line is pretty 'meh' so I'll probably pass.
I think Kongo's biggest bonus is from relics/sculpture/artifacts, and that's definitely a mid-late game bonus. You're not getting early relics as Kongo. Great Artists are a midgame GP. Artifacts don't come until late.
As for neighborhoods, I just unlocked them as Kongo. I'm still amenity-limited, which is always the case when I go wide. I had planned to give tall a try this time around, but the turf just begged me to do otherwise.
I don't think they're a bad civ, but at least on the current playthrough, I'm getting roughly zero bonus from them. Too bad. I do think the housing/amenities issue is a real one, though – wide seems stronger than tall, and amenities become more limiting than housing in that case.
Pericles isn't on the original list, though. You might want to fix that.
I'm only listing the stronger leader. Pericles is marginally weaker than Gorgo.
So it's really just the combat bonus that edge [Teddy/US] just a bit above the lowest tier?
US is not in the lowest tier. They are not 'a bit' above lowest tier. The combat bonus is a huge one, especially in the all-important early game. Their other bonuses aren't terrible either. This has been discussed. You're welcome to read those posts.
One problem I have with Russia relates to the tundra start. Sure, you can make great use of those tiles, but your start bias comes with extra barbarian problems. Namely, having to allocate resources to deal with barb camps from the nearby ice tiles that even Russia cannot settle or develop.
Sure, but you'd have to allocate the same or more resources if that were a border with another civ.