I've only played for about 30 minutes since the April update, but interestingly performance has not been an issue for me on my PS4 Slim over the years, with the exception of those things that haunt everyone for a long time now - framerate drop when side panel is open, stutter in supercruise, etc.
Having done a bit of experimenting yesterday in a system that had one of those weird star density anomalies (half the sky densely starred, then a hard border line with the other half of the sky almost devoid of stars) I can confirm that star density definitely affects performance - at least on my standard PS4. Pitching and rolling (in supercruise) over the clear portion of sky = smooth as you like. Pitching and rolling (still in supercruise) over the densely starred bit = slowdown, stutters, pops, even great jumps in movement sometimes.
I know the sky background in each system is accurate, and I love that. I'll also admit I'm not a coder or game developer, but I am a professional TV & film animator and I've had experience of building/generating these sort of environments. This sort of behaviour strongly implies to me that the background stars are being continuously generated. Now, if I were making a 'scene' of an ED star system instance in an animation package I might want to generate the stars from the galaxy model at first for accuracy and continuity, but then I'd immediately bake them to a spherical image and use them as an environment map - much less processor intensive (at least in animation, but I repeat - I'm not a games coder). I guess if that's how their game engine works, then that's what they do.
To your last point, I honestly don't think Frontier writes PS4 code anymore. From their website regarding the Cobra engine (emphasis mine):
I'm pretty sure that in Frontier's reasoning, they see the PS4 as an individual platform "without the need to concern themselves with", despite this being far from the truth. I sometimes wonder if they still have a PS4 team for Elite Dangerous.
Okay, then (sadly) that's a very specific Frontier Developments problem. I've not seen that Cobra engine info before. That does seem to imply they do no optimisation at all for non-PC platforms (in the section you emphasised the phrase "unless necessary" suggests only critical customisation to simply make things
work rather than optimisation to make things
better). As a console gamer I read that as "No Frontier Developments game is ever going to fulfil its potential on consoles, nor match graphic performance of games from other developers who optimise specifically for consoles". Disappointing if that's the case.
As PS5 has now been announced as being backwards compatible with PS4 games I wonder what that will look like when we get the first 'New Era' update, which may well be about the same time as PS5 launches.