That's a false dichotomy. The alternatives includes giving each country an equal standing without a veto, votes proportional to the population, or even fully direct democracy by every person in the world, and a million other alternatives I could think of if given an afternoon.
It's absolutely logically valid to think that international coordination is valuable but that the UN is a poor solution for this, and is blocking off a better solution. Recall also that before the UN we had the League of Nations, which had a similar mission but an even worse implementation, and there's a wide consensus that it's good that it was replaced.
These are certainly alternatives but they would take what’s basically an acceptable-ish arrangement and turn it into what’s effectively a world government, and that’s completely untenable.
If liberal secular democracies that respected free speech and private property rights were the order of the day, we might be able to set something like that up, but not in today’s world with today’s leaders, and the UN has to account for all of those differences. That’s why the UN feels unsatisfying and why it will never “lead” the world.
The UN only survives because it is toothless, and the permanent seats of the UNSC are essential to guaranteeing buy-in from members that otherwise wouldn’t allow it to exist.
It's almost as if the UN is the creation of the Great Powers, as a meeting ground where they can coordinate their actions, and is not intended to be some authority that tells the great powers what to do.
I don't know where these people learned alternate histories of the UN as being some kind of force that can keep nations in check.
It was never intended to play that role, and the UN Charter forbids it explicitly.
The real problem with the UN is that it is obsolete even for the role it was empowered to play, because with the advent of videoconferencing and abundant communication, it simply has no meaningful role to play. What it has become now is a jobs program where well connected people can obtain diplomatic posts and party in New York while not paying any parking tickets. That's literally all the UN is right now.