I think (read: this is my opinion) the underlying issue with all of this (from a PP/CG perspective) is that FD never really intended for CGs or PP to be direct PvP type interactions. PP was meant to be PvP only in the sense that you can undermine my power and fortify yours, while I can undermine yours and fortify mine. I honestly don't think FD ever intended for blockades to be a realistic game play element. So it makes perfect sense that the game's design doesn't support blockade-style game play. And at the end of the day, blockades are what we're talking about: either blockading a CG or direct CMDR-on-CMDR prevention of accomplishing PP goals (which is just small-scale blockading).
If FD wanted Blockades to be a part of this game, they would not have used the instancing mechanism they have right now.
I think you nailed it. Open players want to stop players from undermining/fortifying by shooting them. But those are not PP rules. If you want to stop your enemies, you must do the counter task, not killing them.