The io may be playing a part as are many other elements, although it's not being fully utilised.
Contrary to popular belief that ssd and io hardware can improve performance.
For eg, with faster ssd and io you will need less assets etc stored in the ram, to only be potentially used.
Like lets say in spiderman you need to store only what you see, where on a slower io system you need to store thr next block also as it won't load fast enough otherwise when the player goes there and you could go left right back or forward.
So keeping more in memory is obviously not optimal.
Ps5 only needs to store the next 1 second of gameplay in memory, give or take.
This means more ram for whats on screen or in active use, which probably means higher asset quality etc. This may explain some of what were seeing or it may not even come into play much yet in these early titles, but it will.
I think its not one thing but multiple, incremental gains all over adding up to a big leap over what traditional paper specs 'should' perform like.
So we have the ssd and io tech, all those bottlenecks eliminated so less waiting, better cu utilisation thanks to things like cache scrubbers, no more flushing the caches which hurts performance Sony evict only select adress ranges meaning better utilisation.
Also faster gpu in all the areas clocks affect, faster caches and probably better caching aka unified.
Probably miss something here but the combination of all these improvements should be making the bigger gains were seeing.
There's also less on the cpu where xbox has to process the io on a cpu core, PS5 is completely free of it thanks to the io tech. Again, only probably a relatively small gain but they add up.
Tye tempest engine being used for physics due it its spu like design is apparently being used in small amounts.
The whole system is about reducing latency and all about speed.
Its ram bandwidth isn't split either, which may be a bottleneck, especially when games start using more than 10gb.
Add into that being easy to develop for and Cerny said its easier to fully use 36 CUs than 48 (in his example that definitely wasn't comparing similarly to xbox design of 52 cu....) when triangles are small ots harder to fill them all with meaningful work.
I think they system has rewritten the rules somewhat and a lot of us knew this from they way Sony eliminated bottlenecks with the io hardware, that was an achievement that isn't easy at all.