The US is responsible for more than 25% of the UN's funding and is ~5-6x more than other members of the Security Council [1]. This is disproportionate to its obligations or its population.
> You seem to believe the UN's job is to advance the US's agenda. (No, it isn't. It's there to allow a forum for diplomacy for all nations.) You also seem to believe that the UN is a bad investment. (That's a highly subjective perspective: what are your stated metrics for such a judgement on ROI?)
Countries are not friends. They are allies with shared interests. That means each country has to derive value from the alliances it participates in. These alliances are strategic. If the alliance does not bring value, the country could and should divest from them. These are foundational principles of statecraft.
> If you believe that the world is a better place with regional hegemons ruling their parts of the world with power as the only metric that matters, I'd suggest building yourself a time machine and going back to the end of the 19th century.
If you believe the world is anything other than that then either you have been fooled by the super comfortable existence insulating you from most shocks that the US has provided, or you wish the world was like this. Truth is it never changed. It is still very much regional hegemons governing their parts of the world. The only difference being that the hegemonic boundaries are not defined by homogeneous geographic regions. If you read the world news carefully, you will realize that all conflicts are tied to the boundaries between two or more hegemons.