Ironically, I'd say the issues you're describing mostly stem from playing Giant maps. On smaller maps there is less announcement spam, and a small civ can be much more relevant. Does one really need to have 30 civs and dozens of cities to micromanage?
Really need? No, but I enjoy it, moreso than playing with smaller maps and/or with fewer civs. 25-35 is my sweet spot for civ count, and I love the expansiveness of gargantuan maps, even when considering the memory and performance implications. While in terms of territory and cities the game handles a multitude of civs well, it doesn't handle the UI/UX well, so it's been a thorn in my side for years.
I will have a serious look at that. Seems to me like either a vanilla or more likely a K-Mod issue. RI never really changed anything meaningful there.
Yeah, I don't think this is an RI issue, at least not directly. RI's impact, in cooperation with my preferred game settings, is in barb settling/revolutions putting more civs on the map than the game was designed to handle. So don't look into it on my account, I don't think RI needs to change anything here. It would just be appreciated if there was a way to customize the max civ count so that we can tune it to our liking. But sounds like one exists, so I'll search the codebase for it.
What different form would that be?
I've given this some thought lately, so this will probably be a long answer, going into way more detail and theory than necessary.
First up: What is the purpose of having barbs settle into civs in the first place? As in, in what way should this mechanic enhance gameplay?
If the goal is to yield a civ that is on fair footing to all other civs, then I feel like it should be present on turn 1. Introducing a civ 300 turns into the game and expecting it to hold against and operate as all the original civs opens up a lot of edge cases and balance issues. I think we see that with the current implementation, where the settling civs get all sorts of resources and bonuses to help them stabilize and sustain themselves, often putting them ahead of many civs that
did start on turn 1. They start with more techs, more resources, and more bonuses than many of the existing civs. This also has ramifications for trade: The more civs settle, the more civs on the map have bronze/iron/horses/etc as an immediate resource, and the more of that resource is then not needed to be traded for, and potentially creates a surplus of that resource in the world if they also have that resource naturally.
For context, I used to play with each of the major civs starting on the map, 31 I think. But after revolutions and barb settling, I reduced the starting civ count drastically because I liked the idea of civs rising up organically throughout the game. But this also meant that many/most civs innately have the basic strategic resources, which leads to the problems above.
So for me the goal with barb settling isn't to have "normal" civs. "Normal" civs can start the game with the rest of us. Settling civs can become normal, but I don't think they have a "right" to be normal, nor that they should get special treatment to ensure they are normal. They have to earn their place on the leaderboard, same as everyone else.
I'd rather approach settling civs from the other end of the spectrum: what role do barbarians play in the game, and how is a settling civ a natural continuation of that role?
Barbs have two purposes in my mind:
1. To apply pressure to the player. In the first hundred or so turns it's just animals roaming the earth that civs might encounter, but which don't enter borders. Then it becomes proper units, who still don't enter borders. A short while later they start entering territory to pillage and conquer. After that they start having their own cities, preventing settling unless a civ conquers the barbarian city first. At each step of the way, the barbarians act to apply pressure to civs, first in contentious exploration, then contentious defense, then in contentious expansion.
2. To provide interesting combat gameplay at times without war. You can play a "peaceful" civ and still go about fighting barbarians, conquering cities, pillaging improvements, getting gold, earning great generals, and promoting units. And I think it's important to provide this. One of the problems with the current barb settling is that once most barbs have settled, any new barb cities will settle themselves within 10 or 20 turns, before civs has a proper chance of interacting with them. That eliminates this utility of barbarians entirely.
So what I would be looking for is a form of barb settling in which the barbarians can continue to apply pressure and provide existing civs with something to interact with.
The idea in my head at current is something like this:
1. Barb settling is a gradual process over a 50-100 turn period. Probably longer earlier on in the game, when civs don't have the capacity to raise an army fast, and less during later eras, when civs more often have standing armies and enough production to quickly raise an army if needed. There's a notice when a barb city starts settling, but they remain a regular barb city during this phase. I know AI can't be coded to respond to such notices, but the AI is gung ho about conquering barbarian cities in the first place, so there's no need to change AI behavior.

This period could start as soon as the barb city is founded, but probably a bit after its founding in the ancient/classical eras.
2. During this phase, a barb city starts building up towards settling. In the past I've pitched having it related to culture output, with more culture meaning faster road to becoming a full civ. I can also imagine a version where it's related to combat, where the more battles happen near the barb city, the more it feels pushed to become a proper civ. There are probably other approaches in this vein. I'm brainstorming still.
3. The conversion to a civ can take several forms:
3.1 An aggresor civ. This is a barb civ entering the world stage as a conquerer and military power. Think Huns, Mongols, Vandals, etc. These settling civs get an aggressive leader, temporary (~100-150 turns) military resources (they'll have to conquer it to continue having it. Maybe they have a personal "greed" quest to get nearby resources), a surplus of conquering units, barracks in each of their cities, and bonuses to constructing melee and siege units. Maybe they also automatically declare war on the nearest civ. They should be a legitimate threat to their neighbors, but also vulnerable to burning out and collapsing.
3.2 A protective civ. This is a civ forming in response to foreign pressures and unifying the people in its territory to preserve autonomy and their way of life. These settling civs get a defensive leader, a surplus of defensive units, bonuses to constructing archers, light cavalry, a walls in each of their cities, and bonuses to building defensive units and culture output. They shouldn't be expanding during their first 100-150 turns, and have negative diplomacy towards other civs who's culture is present in their tiles (or maybe just double/triple border pressure diplomacy penalties).
3.3 A commerical civ. This is a civ that develops into trade empire. These civs get an economically oriented leader, a small surplus of a unique trade resource (like Glassware, but something unique to them, or shared with all commercial settling civs), a fair balance of military units, and positive diplomacy towards their neighbors, with whom they should (hopefully) immediately try to trade.
Once they settle like this, they can operate as normal civs, to the extent that their bonuses allow them to thrive and survive. It's okay if they fail and die out. Civilizations don't only rise, they rise and fall, so it's perfectly natural for a civ to come into play, struggle, and collapse, only for a new one to rise up sometime later (or maybe have a resurgence). Their success shouldn't be something forced by the game, but an impressive feat that has us talking about it afterwards.