My theory would be that most of the transfer is about assets and games have more of a memory constraint rather than a bandwidth constraint in that space
Used to be the case but most open-world games stream in assets nowadays and you can see the lower resolution assets fade out as the higher fidelity assets finish loading on the fly.
In games that want to load fast loading a save game might drop you into a pretty low fidelity world and then start loading in the higher res assets.