Hierarchy (if we're talking about actual power structures, not just forms of organizing that might assign roles or something like that) inherently *is* power imbalance, isn't it?
I don't think hierarchical power structures can be redeemed by slapping accountability on them, at least that's been my experience. Besides, to implement accountability you either negate the "quick decision" argument for needing hierarchy in the first place, or you actually show that quick decisions can be made without hierarchy anyway.