Amtrak trains could run on precise schedules--while probably slowing down cargo--and long routes would still be underutilized because most people don't want a more expensive days long train trip rather than a few hour flight.

Yes but properly speaking Amtrak should have cross-country high speed rail routes and lower costs than flying. Amtrak can't even imagine high speed rail as long as they are stuck renting routes where they are limited to 140km/h, less than half the speed of high speed rail in other countries. Even Amtrak's fastest lines, the Acela in the NE corridor, only manage 240 km/h along one or two sections.