Your suggesting that at 6gbs the SSD will use up all the data on the disk, that is mis understanding and trying your best to suggest fast SSD is not needed.
If your character looks at a house, ps5 can load that house in time takes to turn, its about IO latency and file latency as much as te headline SSD rate.
If you charcter then turns around to look at a tank, that tank can be loaded in very high detai and the house is no longer in RAM.
Your character spins around again, house appears again. You are not burning through data, that is funny.
That is keeping less data in memory and as such you can have mega assets in game.
Other platforms would LIKELY have to preload the tank and the house and keep them in RAM.
That is the potential difference, Ps5 can go crazy with detail, others would struggle with RAM and need to reload more and more..