You're conflating Powerplay with PvP though. And that's not actually true, is it.
Powerplay can be affected by competitive PvE activity, it is not inherently PvP and it is not designed to be.
Remember, like all elements of the BGS, Powerplay is designed to operate between players on different platforms who cannot encounter each other at all, let alone engage in PvP with each other.
No, what I'm saying is that when you are in Open and pledged you can block and log, even though the attacker has gained a significant advantage finding a rival who may hold merits / cargo, making that effort being in Open and finding them meaningless.
There has been situations where players holding merits have been destroyed by other players making an expansion attempt fail.