The lack of a rail alternative is absolutely no excuse to accept and condone poor or substandard service on the part of Amtrak. Of course, the mere absence of a diner does not necessarily constitute poor service, though I would argue quite strongly that it is am important amenity to attract higher-fare sleeper (and perhaps business class) passengers.And riders.I agree there is a difference, but I don't know if Amtrak sees it that way. Because of the parallel route, it's an easy train to "test the waters." But once they have gathered data from the test... I bet more LD trains will lose their diners.
And if you're really not going to travel on Amtrak for LD travel, what are your other options?
Fly
Take a Bus
Drive
What you won't be doing is riding another company's train because ... there isn't one. And if food is your biggest reason to choose the train over one of the other options, I'm guessing the food isn't better on buses or planes. I guess if you drive you can stop at fancy restaurants along the way.
If Amtrak downgraded the California Zephyr to one locomotive hauling three Amfleet coaches - no baggage, no food service, no sleepers - would that be acceptable? Obviously we have no other rail options.