The first "don't have to do it" decision, in this game, relates to PvP itself (apart from CQC, of course, but that's not in-game) and no in-game feature relies on PvP so there's no requirement for any player to engage in PvP if they don't want to. The choice of each player of who not to play with precedes (at the main menu or block list) and may over-ride the desire of any other player to play with them.
But as I described, for Powerplay to actually work you need other people, otherwise you wind up with a sub par CG (which is saying something). In a scenario where PP or aprt of it is Open only, you have a choice to engage in co-op PvP team play- its not forced on you because your control is the pledge toggle.
Powerplay can also be viewed as a drop in/out feature too - and, while some players organise their gameplay around it, there's no requirement for any participant to seek the opinion of others as to how they should engage in it.
Not really, because if you drop out for more than a week you wind up with no rank. If you depledge your vote power is reduced to 1 rather than 5 (after 16 weeks). Its why its a smart move to decouple modules from powers, because then people are playing for the right reasons.
Plus, although Powerplay has no in game leader, there is only one correct mathematical way to play it. Thats why groups have formed, because its intensely complex to understand at both a strategic and team level.
Of those three options, the middle one seems most likely.
If its done well, then I have no complaints. What we don't need though is a second abstracted system- it has to offer something beyond how the BGS operates to justify having a whole new feature.
It'd be one way to reduce the effect of merit sniping, which was raised as a problem to be solved....
But this is the thing you are missing- its got to be engaging and fun. ED is about flying spaceships in sometimes hostile places- which is the definition of Elite Dangerous. Its the paradox of Powerplay too, in that you need players to overcome NPC deficiencies but you feel players themselves are the problem. I know you'll say "PvP is not fun for everyone", but if its in a gated, optional part of the game then whats the issue?
The chance exists for those who choose to play in Open, certainly - and does not for those who choose not to. While one may "have to" play in a certain way in Powerplay in Open, that's a choice made by each player - an optional frisson to their own gameplay.
But again this does not address the imbalance. What you are suggesting is that everyone goes into Solo to 'win', which kills variety because then Powerplay becomes a souless CG- one of the reasons why it nosedived in popularity. In Powerplay choice is an illusion because people on the whole (not everyone) will take the easiest path to be the best.
Back to the track and field analogy, its like one athlete asking another to put more obstacles in their path to win a gold medal. Without a hard rule / boundaries a competition with a goal can't be functional.