Ultimately this is the core problem as I see it - a hierarchical society will always be militarily stronger, practically by definition - and if history has taught us anything, it's that weak neighbors get eaten by their stronger neighbors.

Additionally I think most of these idealized community structures are overly optimistic about the likelihood of a charismatic leader coming along and getting people to follow them, and then not letting them withdraw that power. Anarchists talk about hierarchies without formal power structures, but what is actually stopping someone whose already effectively in charge from turning that power into something more permanent, especially if they've convinced the populace that they want that?

Its happened an endless amount of times all throughout history, and I really don't see why it wouldn't here. Ultimately it just seems like a fragile system that relies mostly on every single individual being perfectly rational and immune to the draw of populist leaders. Aka - completely unlike actual humans