Interesting points, but I don't think the FAQ says that. All hierarchical institutions "embody the principle of authority," it claims. That doesn't mean hierarchy = authority, but there's a close relation.
An example I have in mind is the child/parent relationship. Obviously a big issue, which no doubt concerns many anarchists. But my understanding is there's a legitimate hierarchy involved. That is, up to a certain age, children actually want certain limits imposed on them as part of their introduction to this strange world. Or they'll be unhappier as adults.
Now, I think parents should be mindful of their overwhelming power relative to the child, and anarchist ideas can obviously apply. (And I should make clear I'm not a parent.) But that's different from opposing hierarchy. Maybe more like being an enlightened manager, I suspect... [1]
Or take the notion that this FAQ is read-only, rather than a wiki. There's a barrier between the roles of FAQ author and reader. This may have an impact in our discussion here, as the temptation is to defend vs. attack it, instead of discussing how we might just clarify the page. This temptation is often the case when there's some Important Text out there.
Disclaimer: I realize that a) wikis probably weren't common or even existing when this FAQ was made, b) maybe I'm just being one of those contrarians you always see on the net, c) someone can build their own FAQ, and d) maybe I'm stretching anarchism beyond its limited domain.
Tayssir
-- [1] Incidentally, a CEO told me that management literature often claims that authority over employees is legitimate like the authority over a child. That's the example commonly used. Might be entertaining to consider that when you encounter a "benevolent" manager who knows to rule with a minimum of fiat. ;)