I don't write the UN off as completely as you. It has proven useful for a lot of things. It's just that it has a fundamental flaw. It can only be useful when there is unanimous agreement among the five veto-holders. That makes it quite useful in fighting pandemics and ironing out territorial waters disputes and other stuff where the interests of the big five either aren't involved, or where those interests are aligned. But it makes it useless whenever they diverge.
Unfortunately, just complaining about the UN accomplishes nothing. What we really need is reform.... and I'd start by reforming the veto system. But that's unlikely to happen, since those veto holders don't want to lose their power. Probably we won't get major reform until there's been a major failure -- the same way we didn't get a better version of the League of Nations until after WWII had demonstrated how useless the League was in that earlier form.
Here are some ideas for how to reform the UN, if I had the power. First, I'd have 15 votes on the Security Council -- one each for the seven biggest economies, and one each for the eight biggest populations, with countries that are on both lists (US, China, etc.) having two votes each. This membership would automatically change up every year to the extent needed. The Security Council as a whole would manage executive functions, and could veto acts of the legislature by majority vote. Thus, no individual nation would have a veto. However, using its close alliances, the US would still be able to block most things it didn't want, and push through most things it did what, since its two votes, plus one each for the UK, Germany, Japan, France, and Italy would give it a team of seven votes right off the bat, for most things, meaning only having to win over one other nation for a majority.
The legislature would be bicameral. One house would be filled by population, while the other had one-nation/one-rep. The one filled by population would have elections every six years, with people elected by popular vote.... let's say, one rep per every 20 million people. Big countries would effectively have lots of representatives, while small countries would need to pool populations with neighbors or allies to have even one representative. Any population blocked from holding free, open, and independently-monitored elections would have no representatives. This would force countries like China to choose between letting their people pick their own representatives or not getting a voice in that body. Laws would need to pass both houses and survive veto by the Security Council, but then would be legally binding on any country, with enforcement by universal tariff.
There would also be a world court, and lower district courts, modeled after what we have in the US, with justices serving for 10 years, chosen by the Security Council and ratified by one of the lower houses. Each country would be "taxed" to fund the UN in proportion to its GDP, but with some progressiveness, so that richer countries were taxed at a higher rate than poorer ones. Countries could also negotiate with the UN to provide personnel or land or resource concessions in lieu of currency.
That kind of UN could actually get things done. Power would be distributed roughly in proportion to real power in the world, but without the ability of single countries to block action. You wouldn't have the silliness of the UK having a Security Council seat while bigger economies (Germany, Japan, Brazil, Italy), and bigger countries (India, Indonesia) didn't. You wouldn't have the hypocrisy of countries being able to ignore resolutions indefinitely, without sanctions, simply because they were friends with a veto-holding country. It would be more democratic, too, and would give people who have little power within their home countries a voice outside of them. And it would encourage cross-border cooperation among smaller countries.
