That's a max speed, not an average.
And again, for this fantastical train, we're earning the privilege of doing in 12 hours what a plane will do in 6.
And again, for this fantastical train, we're earning the privilege of doing in 12 hours what a plane will do in 6.
If you factor in all this extra stuff, it looks more like 9-10 hours.
You go to the train station, which is in the city centre. You use a subway, tram or bicycle to get there. You walk in, go to your platform and enter the train. You place your luggage in the luggage rack and take your seat. When the train arrives at your destination or interchange point, you grab your stuff and leave. Sometime in between, staff will walk the train and check your ticket.
No long transit to/from the station. No check-in, no security screening, no baggage drop-off/pickup. It's a train, not rocket science.