No. Until that day we’re an experiment-in-progress. No “successful” about it.
Experiments are declared a “success” when they come to an end.
As @Exapno_Mapcase has said, and this is his profession, unlike yours or mine, history does show obvious social progress on many fronts. And yes, a bunch of intermediate backsliding has occurred and will continue to occur. Such is the human condition IMO.
How much the USA has served since 1776 as an attractive model for other countries to partly emulate, or as a bad example to be avoided is a very interesting debate, but not the one we’re having here. I will suggest the overall tenor of the last 300 years of history has been away from hereditary royalty. Which can only be good. The Declaration of Independence and the esnsuing war was the first significant crack in that wall that has since turned into a wholesale collapse of the dam of the old royalty-led world. Whether the e.g. Australians eventually cast off their King because of, in spite of, or with no regard for, the sweep of US history is also debatable. That they will do so in the next 20-50 years is all but certain.
Read narrowly, the AE is “Can we build a society not based on political and economic serfdom?” The answer seems to be a resounding yes.
My own sorta bottom line runs about like this.
Conservatives / Reactionaries are satisfied with their society as long as there’s another worse one they can point to. E.g. Russia or China or NK currently.
Progressives will never be satisfied as long as their current society falls short of an imagined Utopia.
With the result that to Conservatives / Reactionaries, current reality is a glass 90% full and to Progressives it’s a glass 90% empty.
IMO you’re so stuck on your perception of 90% emptiness that you can’t see how much less empty it is today than it was when your grandfather was your age.