It literally does have hierarchies though that was a controversial thing among them during the time, they realized just by forming goals a hierarchy would form around how to accomplish the goal. Even if the way you organize is bottom to top, that is a hierarchy which leads some anarchists to break away and form their own anarchist factions which give way to the same problem over and over. You just are choosing not to see it as such, the majority holds the power over their superior officers, that is a form of order. It's not that big of a deal I'm not saying anarchy isn't real but this is common in anarchist spaces. Any form of organization of any sort, is genuinely forming a hierarchy and stops being anarchism. Anarchists start to suffer from the "no true scotsman" thing.
Anarchist political theory. It is a well fleshed out idea that has all of the traits needed for long-term stability
You realize this is a bit of a contraction? A well fleshed out idea does not equal long term stability unless it does in fact create long term stability. Maybe in theory but as time went on anarchists took positions that placed them above others; police captains, government positions, even if it was just social where one anarchist was seen as smarter than another that is forming a social hierarchy. Saying it is a well fleshed out idea with long term stability is like me saying my well thought out d&d campaign is going to be completed solely because it is well thought out, it's neglecting the reality that other's autonomy actually can directly lend to its downfall. Hell even forming a plan is even slight steps away from anarchy, which they understood and constantly debated over.
You genuinely cannot have anarchy, it is only in the face of a differing usually opposing hierarchy can you engage in being an anarchist and practice anarchy.
This is why many anarchists started embracing socialist tendencies, because their anarchist goals ended up forming socialist systems. You can totally form systems with the mindset of reducing a hierarchies power and aiming for anarchist goals but again, it soon becomes not anarchy once the system is formed.
Convincing a person isn't really relevant to what I'm saying. My whole point is revolutions always start off strong and once the need to handle a system appears, it's not seamless typically kinda dangerous and often extremely prone to issues because being well thought out is only just that, it doesn't suddenly become functional and reliable. When the founding fathers formed America after their revolution this was understood and they tried to make a system that was flexible so as their system formed they could adjust as needed. When the anarchists began accruing power, you see plenty of them fall back into a system hierarchy because that's really just how organization works especially when you're talking about millions of people, then they understand they're drifting from anarchy and they shatter into smaller and smaller groups while the more effective ones with a hierarchy will full steam ahead accomplish their goals and leave the rest in the dust.
I remember learning about this in school, a big reason why the anarchists lost is because they started to collapse from infighting and feeling conflicted about what it meant to be an anarchist and what was required to run a system.
Spanish anarchists specifically really relied on the concepts of situational leadership which directly contributed to their defeat and fascist and communist groups were able to make decisions while anarchist groups were stuck in a crisis of decision making. Power vacuums are inevitable and will always lead to the direct downfall of anarchist movements once they acquire a degree of power. People will say superior outside fascist forces or communist forces but the reverse to that is inferior, slow moving anarchist forces that failed at the one thing that wins wars and battles -- logistics. It's much easier to unite anarchists when they share a common threat.
At the end of the day anarchy in all forms in all goals is directly made to destroy a state or hierarchy and abolish a power structure. Once they do, a power vacuum forms and whichever in-group holds the most power or can organize the fastest will overtake the general anarchist movement and no longer be anarchist. Anarchy is like an ouroborous by nature.