Problems with generally beefed up NPC's:
Rank progression is automatic in Elite. Play game long enough and your ranks do go up. It is NOT same as opt in difficulty level selector.
Something like Thargoids are still opt in stuff, you choose to join the war against them. Not so if general NPC levels are upgraded. Unless we talk only about PP or certain high grade missions.
I think that's more a "general" problem: difficulty should be calibrated not considering ranks (which is just a linear progression, you donpt have to be particularly good, you just need to be sturdy and play a lot), environment should be the most important factor in my opinion.
For example, system security levels should be a factor in spawning high ranked lawful and unlawful ships, then if you are a low experienced lawful/unlawful player will be your choice to try do your stuff in more or less difficult systems. I wrote some thread about it in the past if I remember well, bit I do not want to go and check where it is honestly.
I think that more than difficulty "per se", it should be important to balance personal rewards and consequences over the environment (being them both BGS and Powerplay) considering the actual difficulty of the action completed (and the time such action needs to be completed).
That would mean a complete rethinking about how rewards are administrated right now in Elite Dangerous, and I think it would make it more challenging, exciting and finally more fair (and less grindy, which is most important imho).
Considering Powerplay alone well... you did the example with Thargoids, which are, as you said, completely optional.
Powerplay is optional too. You chose to pledge for a Power even for some modules, but that's not mandatory, that's optional. You can still play the game even without never being pledged.
If you think about it everything is actually optional in the game.
But that's sheer "philosophy" eheh.
The key element that I always hoped FDev would have considered some point (and they never really did sadly) is balancement, that's all, the real core problem in Elite Dangerous that we deal with since Horizons (first vanilla ED was far less unbalanced, but it was a much simplier game too, with far less features, s oit was easier to keep the personal progression decent, for example).
But I am afraid we are really going out of topic. Even considering the sub-argument (Open in Powerplay).
I think that one of the key features fdev should address is the effects of system security over gameplay, making almost impossible for unlawful or wanted players to even fly in very high security systems if they are wanted by that jurisdiction and on the other side making extremly dangerous for players to go in low security ones, of course leaving the possibility to survive, giving high rewards to both if they succeed.
