Past performance is no indication of future success. It doesn't matter what's been successful in the past, these things can change. Communism was considered more successful than capitalism for a large chunk of the 20th century (because it was), then that changed and so did the narrative.
None of this is settled, because it's a living system that changes over time. What may have been perfectly true in 1850 might not be remotely accurate in 2050.
> 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.
> Communism was considered more successful than capitalism for a large chunk of the 20th century (because it was) According to whom?