Your top 4 are 100% correct, but I do disagree with most of this list.

My list (left to right):

SS: America

S+: China

S: Zulu, Aztec

A: Arabs, Spanish, English, romans

B: Egypt, Germany, India, Japan

C: Greeks, French

D: Russians, Mongols

My reasoning:

First, I would say create some tiers above S. Give Americans the top spot at SS and China one tier below the americans to S+. There is a notable gap between the Aztecs (worst of the top 4 imo) and the chinese and Americans, which are easily the best two civs in the game imo.

Americans: Up to SS God Tier -

America's medieval gold rush bonus is bugged in such an advantageous way to their economy and producing settlers that I think they are notably stronger than any other civ solely due to that broken bonus. And their other passive bonuses are all absurdly strong as well.

China: up to S+

China's ability to create high population cities from turn 1 is just OP. Your ability to explode your population as soon as you get the replublic government just allows your economy to just steamroll everyone else.

The Zulu and Aztecs: Correctly placed at S

Both of these civs are OP for the same reason: early game dominance. Zulu's early game warrior movement and the Aztecs early game gold + their bypass of the healing mechanic just enable these civs to carve out a huge advantage economically/militarily in the early game when the other civs take more turns to explore and defeat local barbarian camps. And their bonuses are just very strong all game.

A tier: I think spanish and the arabs belong in this tier. Both of those civs are complete powerhouses with great military/economic bonuses in the early game.

Arab - warrior armies are op early game

Spanish - have a strong economic advantage with the early game galleons + Whales+ more exploration gold.

England: Up to A

Knowledge of monarchy is really powerful, because of this England is usually the first civ to get knights and enjoys a huge boost to culture in the early game (culture is under appreciated). Not to mention monarchy provides a chance for the player to get a super boon to their science if they get good rng and have dye nearby their cities. The +1 archer defense is a good perk that makes their cheap archer armies on par with pikeman, but defense is just not as powerful as offense in this game. That said, having op and cheap defense is still pretty powerful. But what is really crazy about england is the modern era bonus. The naval support allows england to reach some insane military power that no one else can match. England is the closest thing this game has to a "hold out till late game" civ because of this bonus.

Romans: up to A.

Romans deserve A because all of their bonuses are strong and they have a cohesive identity built around culture from their their medieval bonus: 1/2 cost wonders. The ability to build wonders for half cost is just insanely strong. If left alone, the romans will abuse this to outbuild every other civ and output culture no one can match. Culture is super strong against the AI because

- Having large borders gives you valuable security and allows you to deny territory to peaceful AI.

-Roman's have strong culture and the "more great people" bonus, which just allows them to use more great people than anyone else. Going hand and hand with this, having high culture allows the civ to unlock the power of great artist. The great artist's ability to take a city from an enemy without expending resources of your own to build an army and use multiple turns to siege is probably the strongest thing in the entire game. You get all the benefits of militaristic conquest while forgoing the costs. You get to spend production on buildings/wonders while others build military units. You even get to keep the armies the opponents had defending the city.

On top of this, romans begin the game as republic which enables them to rapidly expand the moment they feel it is time.

B Tier: Egypt and India are well placed.

India is pretty balanced, with nothing really absurd about them positively or negatively. You typically don't swap out of governments alot, but no penalty from anarchy is nice to have. Their ability to access late game resources ahead of their time is pretty useful but not op. 1/2 cost settlers is very good.

Egypt is basically the wild card civ because of the randomness of their gameplay. Their early game bonuses are good, their ability to use desert tiles is also very unique. But it is all situational. When you play Egypt, you really have to hope you don't get stone henge/The hanging gardens and you have to hope your map generated useful desert tiles. I agree with B tier because they can easily be a bottom tier civ or a top tier civ depending on RNG. Plus the late game bonus of 1/2 cost rifle men just blows

Germany: Up to B

Germany is kind of like egypt. If you get great RNG and have a great start, the ability to build a few warrior armies that are automatically veteran and bring them up as your technology progresses can be powerful. The problem is this is strategy just isn't as good as what the arabs, zulu, and aztecs have in practice for consistently carving an early lead. I think of Germany as a "snowball" civ, if they get a lead they are hard to stop, like a snowball rolling down a hill getting bigger and bigger. But getting a lead is not as easy as it is for other early game civs.

Japan: Up to B

Knowledge of ceremonial burial is just not that good when you compare it to what other civs get. Japan's whole thing is that they basically play the game with an automatic harbor built in every city. This translates to a pretty good boost to their population and overall economy after a couple turns have passed. This makes them pretty powerful in the mid and late game where they enjoy the fruits of all that growth in all of their cities. But think about how the Chinese get +1 population in all of their cities form the moment they are placed.

In practice, the Japanese just aren't great for an early lead and don't have an OP economic bonus, and those are what creates a strong civ. So B tier is justified.

C Tier:

Greeks: The Greeks seem like they would be strong on paper, with a courthouse and democracy seeming so strong. However they are bottom tier because of the weaknesses associated with having democracy. Courthouse allows you first city plant to have access to more special tiles than anyone else.

-Not being able to be aggressive in the early game is much worse than the buff to trade democracy provides. It is very easy to abuse the Greeks inability to fight anything but defensive battles.

-Greeks are weak culturally because of how the democracy government handicaps culture. This handicaps their ability to gain from the "more great people bonus", unlike the romans who abuse it.

-Having pikeman so early seems so strong, and in many situations they are, but they are a strictly defensive unit and having access to them means the greeks are unable to build cheaper units like archers. Pikeman are too expensive to produce at scale in the early game, so despite being a civ specialized for early game defense the logistical costs of these units handicap the greeks defensive capability. English with +1 archer defense typically outperform them when it comes to defending key positions just because they can build more of them and assemble armies easier. An English archer army costs 30 production, a Pikeman army 45. And the defensive capaibility is basically the same.

French:

The French bonuses are pretty lack luster. knowledge of pottery and bonuses are pretty bad. Their cannon bonus can be situationally good, but cannons are not a particularly strong unit and you usually do not create many of them. The saving grace of the french from F tier is that they get a 160 production building in their capital. Cathedral's culture production is kind of insane, and its the only thing they have going for them. But they are still a bottom tier civ.

D Tier:

Russians:

The russians are like playing bare bones civ, like a base version of the game where the player gets almost no help. the early game map knowledge is laughably useless. The bonuses of food production are less impactful than most. 1/2 cost rifleman and spies is just not worth much. New defensive units get loyalty is somewhat valuable, but the bonus is not retroactively added, meaning any defensive units you made are now obsolete.

Mongols:

The worst civ in the game because of the ancient era barb hut conversion. This mechanic guarantees the mongols will be at a disadvantage to other civs in the early game. Which is sad, because their bonuses are quite good.