And I think that's generally true in everything, everywhere. The reason you can walk down the street safely in most places is not because of an implicit agreement of cooperation, but simply because we're all working in our best interest. You don't even consider messing with other people, because you'd just end up in prison for negligible gains. And indeed as soon as that threat and imminence of harsh consequence disappears, it suddenly becomes much less safe to walk down those streets.
BRICS is not united in some ideological conformity, but instead in self interest. They don't want to be dominated by a single hegemon. And I think this form of cooperation based solely on self interest - is far more likely to persist and yield fruitful results. I also expect this is why agreements will, and should, take much longer. Instead of just bum-rushing some virtue filled "Treaty of Whatever" that'll get scrapped by any participating government when it becomes inconvenient, they want to ensure there are implicit self-interest motivated systems driving cooperation through any foreseeable circumstance.
Their primary complaint is that they wish they were hegemons, except to them hegemony means being far more of an asshole to those you dominate than the US's terms. Thus their need to try to force the issue rather than naturally ending up in that position. This is also an issue India and China would conflict on, as being neighbors, they seek to be hegemons over the same region.
They're talking about moving past the USD, but none of them have the trust and general guarantees it has had and none of them are going to risk putting their trade in a currency that would be dependent on the whims of their direct competitors.
I also disagree with your premise that this is comparable to nuclear deterrence. While nukes have been a deterrent to conflict between the US and USSR, Europe and USSR and perhaps also between India and China, they haven't really been a large factor at all in Europe and in Africa.
I think they've been comparatively peaceful not because of nukes, but because European countries were forced to come to terms with the futility of trying to be hegemons over each other over both world wars, with the second one having finally been brutal enough to make them give that up. Now as WW2 fades from living memory, they remain peaceful due to deep integration between cultures that makes it difficult for them to "other" another enough to justify war.
The world order as you know it today is not even remotely "natural." And this is a fundamental component to try to appreciate the geopolitical relations between countries, as well as how other nations are going to perceive the various threats of the world.
[1] - https://en.wikipedia.org/wiki/United_States_involvement_in_r...
[2] - https://worldpopulationreview.com/country-rankings/how-many-...
In Yemen, the US-led airstrikes have bombed hospitals, markets, etc. as recently as a couple years ago, leading to the largest humanitarian disaster in the world: https://www.washingtonpost.com/investigations/interactive/20...
In multiple countries across Africa, US-trained officers have led numerous coups: https://theintercept.com/2022/03/09/intercepted-podcast-afri...
Yes, it's true that USA seems to have stopped overthrowing governments in South America (if you don't count the coup in Honduras, or our upcoming invasion of Haiti). But countries across south America remember the decades of overthrowing governments and installing our puppets there. And countries across Africa are seeing it today.
Collectively, the "global south" and the "middle east" doesn't have a great view of the USA. So it's not surprising that many of them are joining BRICS as a way to have some allies against US aggression and hegemony, or at least counter its financial dominance with the dollar, world bank and IMF. It's not unlike the governments of countries that experienced USSR's aggression and hegemony seeking to join NATO, in order to have some allies against USSR, and now against Russia. It's not necessary for all their interests to align, in order for some of them to align. "The enemy of their enemy is their friend", is very much in play here.
But you can go further, beyond governments and politicians (as I like to do) and look at polls of regular people around the world. It's not very favorable to USA. Not just "years ago", but let's just look at the last 20 years. The public in our allied countries in Europe named USA as the greatest threat to world peace:
2002: https://www.pewresearch.org/politics/2003/12/10/anti-america...
2007: https://www.ft.com/content/70046760-27f0-11dc-80da-000b5df10...
Across the rest of the world:
2014: https://nypost.com/2014/01/05/us-is-the-greatest-threat-to-w...
2021: https://www.theguardian.com/world/2021/may/05/us-threat-demo...
2022: https://thewire.in/world/more-indians-hold-us-nato-responsib...
2007: https://www.ft.com/content/70046760-27f0-11dc-80da-000b5df10...
There are plenty of legitimate criticisms of US interventionist foreign policy, but that is largely irrelevant to the global trading system. Money talks, and most of the countries with money (or goods worth trading) are at zero risk of a US invasion.
As for Niger, it's not a member of that bloc nor has it even been invited to join. Regardless of how much uranium they export, they will never have any influence over the international financial and trade settlement system. So, I don't know why you would even bring that up.
BRICS is not about cooperation, but rather about allowing each independent country to fully pursue their own self interest. Right now that's not really possible when relying on economic systems controlled by the US. So we're seeing a gradual shift on the currencies countries hold, US debt holdings, the development of e.g. SWIFT alternatives like SPFS, and so on. The development of a common currency will be the next logical step.