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.