I've noticed that too. I think back then they were still designing things using the philosophy from prior Civ games, where the bonuses were more simple and subtle. Hence why most vanilla civs had abilities that were good, yes, but nothing that makes you jump out of your seat and exclaim "that's OP."
Back then, I think Civs were always designed in a very "soft" and non-forceful way when it came to their abilities. Rather than forcing you into a playstyle with strengths and maluses, they all just subtly encouraged you into playing a certain way, but still ultimately leaving the choice up to you. None were particularly flashy, none required you to play a certain way to make the most of them, and few of them had maluses or direct synergy with the rest of their kit.
The only exception would really be Kongo, as they were the only base game Civ with a malus: no founding a religion. Even then, it seems like they were created with a different design philosophy entirely when compared to the other vanilla civs. Most vanilla civs had no direct, non-conditional number bonuses. Even things that were close (Teddy's combat strength, Pericles and Gorgo's LAs) were still conditional and required a specific circumstance to be triggered. Kongo was the only civ in the game that said "have double great people points, non-conditionally." But Kongo's more asymmetric, synergistic and... for lack of a better term, "obvious" design seemed to be the formula civs would try to imitate afterward.
I see the vanilla civs (excluding Kongo) like this: you're ordering a meal from a restaurant. And of course, there's a main course, but that's not all you have. There's plenty of small sides and beverages that go along with it. They may not be directly tied to the main course, but they're still part of the meal. That's what Civ VI's original design philosophy was: in each civ, the player would be given a main course and some sides.
But with Civs like Kongo, rather than having a diverse meal made up of smaller, unconnected parts, you were simply given a giant main course, doused in seasonings and flavorings. There was only the one main course, and really, only one thing to eat. But, that one main course has so many things working toward it that it may very well be the best thing you ever taste. Does that make it an overall better meal than having all those side dishes? That's up to you. But the "single main course" ideology was what the Civ team designed everything around from then on.
In the single DLC packs and Rise and Fall, we began to see that transition in design. Most civs felt more like main courses, and if they did have sides to open up other playstyles, they were usually not as many. Sure, Persia can go Domination
or Culture, but they don't have an inclination to do much else. And sadly, during this transition period lots of... gimmicky abilities started to show up. Particularly with all the stupid Cassus Belli abilities. Cyrus, Chandragupta, Robert the Bruce, Tamar, John Curtin, and probably more that I'm forgetting all had abilities tied to different types of war. Personally, I hate it, and it takes up the slot of what could have been an interesting ability with more applicable use cases, but that's entirely my opinion.
The general design of civs hadn't
entirely shifted over to that main course mentality, but you were definitely starting to see a lot more refinement in their abilities and playstyles. You weren't getting nearly as many sides. But, when things truly transformed was when Gathering Storm released, showing off lots of hyper-focused civs with specific playstyles who weren't very lax about you not playing to their strengths. No longer were you given little sides- everything in a civs kit had a specific purpose for what they were meant to be doing. "Wait, how does a cultural diplomatic civ make use of a combat unit when they can't declare surprise wars?" "Simple: it makes National Parks for you." "What use does Mali have for an offensive military unit? They already have enough gold to purchase what they need." "Well, it gives you gold on kills." "Hey, why does Hungary need a bonus to districts anyway?" "So you can develop your crucial Domination infrastructure to be ready for your levying timing attack."
Everything in a Civ's kit now had purpose. And, this is when playstyles became more forceful. As Mali, I
have to purchase the majority of my infrastructure. I don't have a choice there- the production penalty is steep. As the Maori, I
can't remove natural features, and I
have to start in the ocean. Even in cases where the unique playstyles they offered weren't reinforced by maluses, you have to remember that every civ is a main course now. Even if you wanted to do something other than what they are specifically meant for, you have no sides to encourage it. Sure, I could go for a religious victory as the Ottomans, but I'd just be wasting my time, as they have zero bonuses to anything other than conquest and siege.
This main course mentality has a twofold effect on the game:
- Civs are now much more hyper-focused, carefully tooled experiences and provide unique, synergistic games that you couldn't find elsewhere.
- Civs are now less forgiving to other playstyles, and somewhat bottleneck you into playing the way they encourage.
Does that mean that the main course mentality is better than receiving a bunch of sides? I don't know, that's up to you. But what I do know is that we've watched a visible transformation in Firaxis's design philosophy over the course of Civ VI, and I fully expect that if/when we get a Civ VII that the new Civs will fit the main course mentality.