It is totally possible that there are still some hiccups etc
simply because the engine / code was never adjusted to the PS5 hardware.
So even if the PS5 hardware should have the power of the Pro x2 or 3 or whatever
its still possible that there are bottlenecks in the game engine itself
or the code doesnt know how to handle 100% of the hardware.
Its not a official PS5 version, its just a game that can be played on PS5.
Its the same on PC. You can buy a brand new 4000 USD PC now and then play some
game from 2007 or whatever in forced high resolution mode etc and it is possible that the performance
will be really really disappointing, way worse than a modern demanding game,
because the older game was never adjusted to this hardware
and it cant magically recognize the newest technology like GPU clock or number of CPU cores.
This brute force mode has its limits, it cant skip or ignore fixed parameters of the code / engine,
its just trying to push the limits of the original game, as much as the game allows it, without any new adjustments.