> Communism was considered more successful than capitalism for a large chunk of the 20th century (because it was), then that changed

The word you're looking for is "collapse". It's when something is stable at one point in time, but then later breaks down. That's what "changed". It wasn't random like weather or something. The economic systems collapsed.

> None of this is settled

The fact that it has happened numerous times in different parts of the world makes it pretty settled in my mind.