Well, benchmarks ... if not running a while, benchmarks won't tell you the full story.
nvme drives tend to not holding their speed very long. Overheating is issue no 1. No. 2 is, to small cache, ...
The Problem for sony is, they can't get past the internal IO of the nvme drive. To equalize that, it must be faster. But after all I've so far seen, I doubt that the ps5 drive can (or must) hold the speed at all time. Doesn't really make much sense that the drive should hold the speed for a longer period of time. Most times games should just quickly load something and than the drive has time to cool down a few ms and than the next load begins. It should not be the case, that a game loads data over minutes at full speed, at least I don't see a use case for something like this. Small bursts of data-streams would be more than enough.