Currently Solo and PG lack NPCs that are equivalent to other players- so solo allows unfettered runs, while PG allows easy x4 CZ grinding. Because of that, Powerplay only really 'works' as a system when its in Open given the way the threat of other players tempers such min / max gameplay.Not as it is currently, it's indirect with possibility, but no requirement, for direct.
It remains to be seen how it will be for Powerplay 2.0 - we just have to wait until September, I guess.
This has been made worse over time given Open had a PvP line with piracy (which as you know was taken out).
Its because you have this inconsistency PP does not operate as it should or provide something above the very basics of very early ED PvE.
PP V2 has many nods to PvP- it lists it in the UM area as an objective, strongholds have areas that need defending and that the devs explaining it always spoke in the context of other players. We also have the curious inclusion of SCO ships and drives too.
It remains to be seen how much of a threat NPCs pose- if PP V2 is to be truly pan modal NPCs need to be capable and deadly, otherwise its repeating the same design error. Given how granular V2 seems to be (as in, its a per system fight) its certainly possible design wise. Weighting is also an option, while crude it does offset the risk.