Roman empire fell not because other weaker nations were too strong, it was because of widespread corruption at that time, it basically finished itself.
USA does have its own problem, including corruption. However, USA's problem is far less severe than other nations including China. US's social order does have mechanism to regularly clean itself of worsening problems, although unable to clean it completely. For China to surpass USA, it must come from advancement in social order itself, most importantly, establishing near buffet-proof legal system and near 100% efficiency in utilizing its human intelligence. Basically, in the area of legal system and efficiency in exploring human knowledge, eventually leading to world dominating innovation, China scores quite a low point here. It has a very long way to go.
USA does have its own problem, including corruption. However, USA's problem is far less severe than other nations including China. US's social order does have mechanism to regularly clean itself of worsening problems, although unable to clean it completely. For China to surpass USA, it must come from advancement in social order itself, most importantly, establishing near buffet-proof legal system and near 100% efficiency in utilizing its human intelligence. Basically, in the area of legal system and efficiency in exploring human knowledge, eventually leading to world dominating innovation, China scores quite a low point here. It has a very long way to go.