Earlier quoted context omitted.
Exactly. I had this exact thought experiment of "What if America were no longer Hegemon". So, I looked at other historic examples. The British, Dutch, and Spanish. (You can add German/Austrian and the French, close contenders). They're all still very well-off!
What you're missing is the role the U.S. has historically played in preserving and protecting democracy in the world and, particularly, Europe. If America was suddenly no longer a hegemon, it would be qualitatively different. There are other hegemons in the world that would step into the void left by the U.S., and it would be their influence that would be felt most the world over, including by the countries you named…
Another problem (which Trump is idiotically pushing) is for everyone else to grow their military. Do we really think the world is safer with more countries having larger militaries that are an election or coup away from no longer being allies?