Well, I've got Mixed feelings on this one. In principle I wholeheartedly agree that PowerPlay has to be open Open Only, this game mode really doesn't work with the other modes being able to circumvent it. Yes you can argue that that's not what Frontier promised (The statement that MB said that all modes act equally on the BSG) but when the game mode is broken because of those game modes, then surely you do something about it. I'm quite sure the rewards that powerplay gives you could be earned in another way for Solo/PVT group players.
By Extension you could argue the same for the BSG that only actions carried out in open affect the outcome. However, I remember that there is a lot of background calculations in the BSG which doesn't take Player actions into account. I.e. the amount of NPC trade which is calculated for every tick. It means player action doesn't have the same impact as it does in powerplay, (even though it is a more popular mode).
The one thing that people don't like me saying is that I also think that CG's should be Open Only as well. In a perfect system, player's should be able to challenge a CG that they don't agree with and be able to blockade a system to try and prevent a CG. But I understand that would exclude console players who haven't paid they Multiplayer Sub (or should that be their Extorsion sub) and exclude them from gaining the same rewards.
And to be honest, until they come up with a solution to stop or punish combat logging, the arguments for or against the modes are all moot anyway.
Conflating the BGS with PP in your opening paragraph isn't helping your argument.
The BGS was designed from the start to be influenced by all players, in all modes from any platform.
This has never been debated for change as Frontier have firmly states this is what they want.
Same goes for CGs. They were designed around the mode system for everyone to enjoy, not just gankers.
And if Frontier want a system blockaded, it will be - that was never a choice we were ever going to be given.
PP was debated, the initial response from David Braben was;
Unlike community goals, Powerplay is a swinging balance - ie solo players are also balancing solo players.
Without any proof to the contrary and without any more statements, we have to take this on face value.
Sandro Sammarco since then asked the community some questions about our views on Power Play.
Nothing has happened since then, apart from some clarification that he was only talking about Power Play - as some people got over excited and saying the BGS was going to be mode locked.
So Sandro had to correct them and point out he was only ever talking about Power Play.
Sandro also pointed out that most people (by a significant margin) play open. So why do we need open only content, when so many people are there anyway???
All in all, making content Open Only does not solve the inherent problems with PvP.
All it does is annoy anyone who uses and enjoys the game as it was made, advertised and sold.