PS5 ssd speed is very much exaggerated. The speed is more like our normal sata ssd. To people who only play console all their life though you can described as super blazing fast ssd, which is true compared to the HDD used before.
They test it and the internal ssd is slightly slower than external sata ssd.
You misinterpreted their words. Those old games are designed for at most, someone upgrading the PS4 to a SATA SSD. Thus the games sometimes favoring SSD and thus, getting you faster speeds. That is why ideally, just keep your old PS4 games on an external SSD drive.
But ACTUAL PS5 games that will really take advantage of the NVMe will be way more impressive. To the point where it can even beat PC game loading times as well. I have NVMe SSDs all over my PC. So I know. Anyway, once Microsoft brings DirectStorage API from the XBOX to Windows, then finally, PC should in theory be able to match the loading speed of the PS5 games.
The upcoming Rachet and Clank PS5 game will be the best example of the PS5 game loading capability on that very speedy NVMe SSD.
PS. Currently on Windows, some games actually load faster too when you are using a SATA SSD vs NVMe SSD. And again, it boils down to the coding done for these games to take advantage of SATA SSDs and were not designed for NVMe.
Thus the need for Microsoft to include the DirectStorage API.
So as you can very well see, the PC is suffering from the same problem that the PS5 is facing as well. And it all boils down to the games having to specifically be able to take advantage of the way faster speeds of these NVMe SSDs.
The video to prove this is on Linus Tech Tips in regards to comparing the different SSDs.
And with Rachet and Clank technical analysis out, the verdict is clear at how fast and almost instantaneous the loading is from the PS5 SSD.