It depends what you mean by as large scale - hierarchyless civilisations have happened at the scale of millions of people - over the area of several combined countries if we take the example of the Indus Valley civilisation or Zomia.

As Gall’s law says, every complex system that works evolved from a simple system that worked. I wouldn’t characterise the current world’s system as working well- if it all - for the majority of the people under it. But for me it is as much a moral question - what entitles, justifies or qualifies someone to rule over someone else?