Engels claims organization requires authority, but it really only requires agreements, coordination, and sometimes rules; a strict hierarchy isn’t a necessary requirement for that to exist.

Yeah, horizontal organization has been very effective historically and definitely doesn't create unspoken hierarchies that are actually far more damaging than explicit hierarchies under democratic control by the masses.

There's definitely a single example in history you can point to of that working that won't make everyone laugh as they post long winded essays about exactly how hierarchy was enforced in whichever organization or area you choose as an example.