If US hegemony ended today, it would mean immediate war between Saudi Arabia & Iran, China & Japan/South Korea, Russia & the former Soviet states, and probably China & India eventually. The US is far and away the most powerful military in the world, and without the threat of the US military intervening on behalf of its allies, those conflicts are nowhere near as one-sided as they are today.
For example, see what happened as the Ottoman Empire & European colonial empires collapsed at the beginning of the 20th century. Then scale that up from a 2.3 billion global population to 8 billion.
Whatever you want to say about the crimes against humanity committed in the maintenance of US hegemony, I will agree with you, but that doesn’t mean for a second that the alternative is better. Be careful what you wish for and all that.