Yes, a cruise offers a much better value at a much lower price.A cruise will have thousands of cabins to fill and a workforce comprised of people from third world countries who make a pittance, far below US wages.
An Amtrak train will have at most 10 bedrooms under current conditions and 15 back when some trains had 3 Superliner sleepers. There will be as few as 2 bedrooms on some trains. Amtrak OBS is provided by a relatively well paid unionized work force with a good benefits package.
I think those simple facts speak for themselves as far as comparability goes.