I agree with some of this. But the final conclusion not so much. What country is better than the USA? Where else would you rather live? As long as the answer is nowhere else, then the experiment has succeeded even if it hasn’t lived up to the highest potential.
There is an argument that the expansion to the West extended the experiment.
There is an argument that technology created new variables that the founding fathers did not foresee and thus did not safeguard against.
I do not think either of these arguments mean the experiment failed. The experiment seems to have worked well. Sounds like we need a new experiment. Perhaps it will happen on Mars.