On pc we have never had any download and update while in standby. It has never been an issue to be fair, steam schedules updates and so does windows. W10 automatically 'knows' your times of active use and updates are installed accordingly. I have a 1gb/s connection and a fast pc/nvme, never had i have to wait for an update somewhere. If XSX has a system equal to that i dont see the issue.
That changes when people are on slow dsl connections though, you'd have to leave the 29watt xsx on the whole night or something.
Another thing, W10 is never really in full shutdown, even if you press shutdown the system is in some kind of resume state. Hence the uptime in taskmanager counting every second since the first start, even the times the pc is shutdown. Probably the reason why booting only takes a second.