Great topic - we've still got a mish-mash between the two 'styles' described here, with growing emphasis on non-action / non-'directive' (to use your term) purpose statements.
The way we've been framing this internally is along the lines of a Mission Statement, which has Vision + Action = Mission, as something we often work on in our organization's personal growth workshops and peer support groups.
Vision = the way I wish the world would be
Action = the things I will do to work towards that
Holacratically, then the adaptation is:
Purpose = the way the org / circle would be if this Role was fully expressed
Accountabilities = the recurring actions the Role takes in pursuit of that end state
We have found the differentiation to be very helpful in providing role clarity and dilineating a 'reason for being' from 'what I do'.