There's no doubt we can imagine a dominant world power that would be a lot worse than America, such as if the Nazis, or imperial Japan had won Second World War.
At the same time it is surely possible to imagine, and hope, that America (and its allies) could be a much better influence on the world, by not exploiting the resources of weaker nations, propping up tyrannical dictators and regimes, and overthrowing governments.
China is the most realistic and relevant alternative. Which is scary from a western perspective because they don't seem to share our notions of individualism and freedom. But this doesn't mean they are without values. In the place of individualism they seem to value community, collectivity and authority.