As soon as the game launched with the three game modes PvP was as it remains, an optional extra - that was in late 2014.
While it may be considered by some to be intrinsic, it wasn't - as no game feature required it, i.e. it was and is not essential.
You say optional extra, I say intrinsic feature that required a great deal of effort to avoid.
Open was (and might still be) the most popular mode by a wide margin and I imagine most people playing MMOs, even first person fantasy space flight ones, were expecting to encounter other players. In a game where one can harm those they encounter, it's pretty difficult to cleanly separate PvP from the Open experience.
Losing progress, i.e. credits, due to overwhelming NPC attacks, and the speed with which it was fixed suggests that Frontier looked at the gameplay stats and did not like what they saw.
Ah, that kind of backwards.
Yes, players tend to be risk adverse and intolerant of even the vaguest possibility of failure...which is surely why that whole 'cutthroat galaxy' thing is a farce.
Reduction in repair costs also probably fall into that category - as it got to the stage at one point where the perceived wisdom was to self-destruct rather than repair the ship.
My first trip to Hutton orbital cost ~10% of my CMDR's net worth in wear & tear and was almost the same as a rebuy. That said repair costs being more than replacement wasn't implausible, and if undesirable could have been addressed without making it completely irrelevant by cutting costs by an order of magnitude.
The first states who affects the shared galaxy, i.e. everyone (so it's mode agnostic), the second tells players that they don't need to play among other players.
It's not mode agnostic, because of the latter. If it were, it wouldn't be more efficient to contribute influence, merits, bounties, or bonds from populated systems while in modes other than Open.
For the Open experience to be undermined, what was the baseline from which it changed? It's only ever been one of the three game modes on offer at the start of each game session.
TTKs increasing (which happened naturally/gradually at first through inevitable demographic changes, but skyrocketed after the introduction of Engineering) and and the log out timer not scaling proportionally undermined Open. Expansion of the block functionality with increased weights against instancing undermined Open. Introduction of PP as a competitive mode with perverse incentives to avoid direct confrontations undermined Open. Run away credit inflation depreciating the value of cargo, most especially of rares, virtually killed 'real' piracy, which undermined Open. Etcetera and so forth.
Edit: Can't forget that massive Engineering grind wall that, despite credit inflation, moved the limiting factor required to engage with other CMDRs on semi-even footing from the time needed to acquire some basic skills to the time required to acquire several hundred G5 rolls...and this was even worse in the pre-3.0 system.
Not wilful ignorance, no. That some didn't read or realise the consequences of particular statements in the advertising is clear though.
I still believe the balance of the statements in the advertising is far more suggestive of the idea that there is meaningful PvP (among a whole slew of other potential that is now lost ) to be had than otherwise.