To my eyes, both you and @nutcase2690 are right about those unclear cases of hierarchies.

Anarchy rejects hard-structured hierarchies, that’s for sure. But if we take a more general definition of hierarchies and authorities, then there is the possibility for more “fluid” hierarchy, both in a good and bad way.

About the good way, i believe Bakunin wrote a passage i like about it in God and the State, pointing out that anarchist recognize the authority of some people when it’s meaningful (like trusting the orders/guiding of an architect when building a house). He also points out that what matters is the possibility to end this authority : it has to be temporary and/or linked to a task, to automatically enable the possibility of stopping recognizing this authority. You’d also have to be wise enough yourself to identify when to give your obedience/trust and to who, and this implies that this is not a precise science, we have to accept that sometimes people will make the wrong call and respect the authority of someone they shouldn’t or vice-versa.

About the bad way, as you pointed out, all this really opens for the possibility of informal majority oppression or leader oppression. One imperfect solution to this is precisely the possibility for anyone to refuse authority at any time for any reason. Another safeguard is to speak about this and call out situations that tend to it and look like it : positive point here, the fact that anarchist and leftists organizations are known and mocked for bickering and splitting perpetually is a sign that they already do this (not great for movement unity though but heh, this is what we’re working with).

There will be no definitive victory and perpetual state of anarchy, we’ll always have to fight against temptations of power structures, especially when they’ll come back in those informal forms once we get rid of the formal ones. But if you can get rid of a state, preventing weaker forms of it should be a walk in the park.