It's just the care and full on focus on integrating this aspect into PS5's overall architecture which goes a step further than in PC and XSX that will allow the PS5 to differentiate itself more significantly on this front. The reason is that, for things dependent on time to load, every second counts in not breaking the immersion of (near) instant.
Sony doubled down on the SSD raw speed, but Microsoft, Nvidia, ... all worked on bottlenecks and made sure the SSD won't be hold back. The
biggest difference is imo the speed of the SSD itself. But when it comes to changes that the I/O can bypass the CPU and go directly to the GPU for example, then that's something everyone thought about.
And this is very good, because having so much hardware out there with great I/O capabilities means we will see a much faster transition towards I/O heavy games than we all are probably anticipating. This is great for all gamers, because third party can take advantage of the new game design possibilities without worrying how many people their game can reach.
I think the fact that even the lightning fast PS5 SSD has to do very quick transitions mean these sequences will also be possible on slower I/O. It will just take longer, which can be cleverly hidden like the Mist in DS shows on PS5. What would happen on PC (with a slower SSD) and Xbox? The mist would take a bit longer to build up.
We have to talk to Bluepoint to get any confirmation, but it seems like the player can't control the game anymore when pressing a button at the portal. Which means everything outside of the players view can already be replaced and refilled with new assets. Second step imo is the mist effect, which not only fits the game atmosphere. But it also ensures imo that they can quickly start to replace more assets as soon as they are hidden by the mist. Third and last step is the ultra quick transition to the new area.
i think the mist is a very, very clever way of hiding the actual loading times, which are still very fast. But not instant as in instant.