Flex dining lunch & dinner is all premade & microwaved or convection oven reheated (depending upon whom you ask) and served in the cooking containers. Breakfast is a limited selection of packaged items. Dessert is limited to a packaged snack, usually a brownie or blondie.
Traditional dining is prepared by a full crew in the kitchen. Some people say that traditional dining fare is also premade and reheated or finished off in the kitchen, but obviously at least some items are cooked to order, e.g. steaks, French toast, and the Artisan Grilled Cheese. And everything is plated prior to bring served.
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Indeed, there was some preprepared and blanched/precooked/Cryovaced food. Mashed potatoes were instant but were the good kind. Corn and green beans were canned/reheated, just like at home. Steaks were semi cooked, Cryovaced and grilled. Eggs were prepared fresh. We even had grits sometimes on the Crescent! I think some of the FSAs would bring seasonings and condiments, including Tabasco A-1, and Worcestershire, when AMTRAK did not supply it.
It was in the main very tasty, plated, as you say, in a very nice presentation.
The original china and silver was replaced with hard plastic disposable dishes, but still stamped metal flatware.Eventually plastic cups, cardboard cups and individual containers of wine, milk, and of course, beer.
Sodas (Pepsi, then - YAYYY! - CocaCola) in cans. An actual cooking staff downstairs in the Superliners and in the galley in Viewliners.
When I was commuting weekly from AUS-FTW, I named the head cook "Chef DuJour", and had an a=engraved tag for him to wear. He never got grief from management about it.
The execrable nuked garbage, lack of presentation and crudity of service nowadays, compounded with overstretching the Food Service Attendants is a huge smirch upon the AMTRAK escutcheon and should be remedied forthwith.