Xbox One games use 5.5GB RAM, not 28GB. So at most you'd be loading a save state of 5.5GB into your SSD and loading a similar amount. This would make it a peak 11GB/s.
Now, unless Microsoft has incompetent devs, which I don't think they do, they would not be uploading 5.5GB into the SSD for each save state. If you have 6 games, that's already 33GB of saved states on disc. They are likely uploading a smaller save game and then loading assets on the fly. This means that their SSD is not outputting 11GB/s total, but something more like anything between 6 and 8.
What we've seen so far is the Series S taking full seconds to load a save game and take as low as 4s to load a save state. Even at full occupancy, that's less than the promised 2.4GB/s raw. Worst case scenario it's actually around 500MB/s.
Now, you don't know anyone saying VA can do 12GB/s? You must have signed up a week or two ago.
Enjoy:
https://www.neogaf.com/threads/xbox...-custom-hardware-decompression-block.1532436/
EDIT: as for loading times, there's a video in a previous thread showing the load times being a far cry from a PC with an SSD. You know why? Because the Xbox Series S/X are bottlenecked to shit, not because the games haven't been optimized. If I find it i'll add it here.