But there is also the ~80 staff manning stations at each end and along the route, and more staff in the control room, the cleaning staff, the people who manually do maintenance checks every single night, etc.

You can get rid of the cleaning staff right now. The terminals will become disgusting and people will stop using them. There is no way around this type of overhead. If you have larger numbers of people passing through, you need cleaning and maintenance.

Your original point isn’t even true - in California there is constant maintenance of the road network and crews of community service workers doing their sentence cleaning trash on the highway shoulder.

Roads still have far fewer staff per mile than railways, however you measure.

In turn, that makes them cheaper.

Lol, that depends heavily what you consider staff. E.g. look at freight, if you move cargo by trucks you need 1 staff member (sometimes called drivers) per truck. Train on the other hand needs only 2 people per hundreds of meters of train...

Even worse for individual car transport. You need one staff (driver) per vehicle...

Is there a source for this? Is this source heavily context-dependant?

Why would there be 8 staff on board? Isn't there typically one train driver and one attendant?

I don't know. They have the restaurant car on some trains so that's another 2-3 people, and I really have no idea about their operation so I added some buffer. I wouldn't expect there to be more than 8 on a train unless it's some special event.

For some high speed routes there’s a limit on how many carriages one attendant can supervise (maybe to ensure timely evacuation?) so a 12 carriage ICE train needs 3 attendants to fully operate.

The staff on board also contribute to keeping the train safe and pleasant - if there’s an unruly passenger, or a washroom malfunctions, I’m happy to have paid a bit extra for my ticket for a couple of people to be on hand to deal with the problem instead of being trapped for two hours.