This is a ridiculous notion. Nobody is going to design a multiplatform game where you're forced to move your character or the camera twice as slow on non-PS5 platforms.
I think the point is that in theory if you can load twice the amount of data into RAM within the same time frame then this would allow for higher quality assets to be streamed in.
Another way of looking at it is that assets outside of the view frustum could be loaded in/out of memory much sooner so the amount of RAM used within the frustum can be higher. As an example slow storage could require assets 180 degrees in front of the player to be held in RAM, whilst a fast SSD may allow something closer to the players FOV maximising the RAM available for what is actually being rendered on screen.