Anarchy is a political structure where there’s basically no one in charge, right? But wouldn’t that just create a power vacuum that would filled by organized crime, corporations, etc.? Then, after that power vacuum is filled, we’re right back at square one, and someone is in charge.
Are there any political theorists that have come up with a solution to this problem?


I mostly agree with this, especially the fact that anarchy may lead to implicit charisma-based hierarchies, whereas current systems relies on explicit hierarchies filled with implicit hierarchies.
I say may because, while you’re right to point out that this has realistic chances to happen, anarchism is also the best tool to point out and attack those hierarchies, even implicit. History of left libertarian groups (at least in France) is mostly a drama of constant scissions and mergings of little groups : while some mock it as a proof of militant puritanism and useless bickering, I see it as a sign that anarchists have a sane tendency to oppose situations where a group could impose onto others, even in most implicit/vague situations.