It’s hard to argue against the longest running democratic system in current existence.
USA is not the longest running democratic system. Even if it were, it wouldn't mean anything.
No, it's not. American politics, especially recently, draws heavy criticism every day in a multitude of newspapers.
There are many other nation-states around the world that have been drawing heavy criticism for their politics. Even ones with different voting systems (or none at all). Such as UK, France, Netherlands, etc. Perhaps it’s not the system but some other factor influencing the current political climate. To me, the fact that political turbulence is occurring worldwide indicates that the issue is not with how one country votes, but likely from some other factor.
The Continental European system with proportional voting and multiple political parties with changing support seems more agile. New parties can form, gain and lose support, not quite as quickly as in one 4-year election cycle, but in about 3 or 4 election cycles the political landscape of a country can change.
But then again, the American democratic system has already had a pretty good run for over 200 years, so can we know if present-day problems are indicative of actual problems in the system, or something that will pass?