The SW Chief has "traditional" dining so what you read here, justifiably complaining about Flex dining, does not apply to it. I consider the current version of traditional better than the one offered prior to COVID, btw. Also the SW Chief retains its Sightseer Lounge.For years I traveled Coach between the west and east coasts on the SWC. Then one night after boarding back in 2010 I became aware that I could book a roomette on the train at lower price. (I boarded in Kingman Ar.) I had a great time and the food was great considering this was a train. In the ensuing years I pre-booked roomettes and had awesome rides on the SWC. it has been now been years since I traveled Amtrak and after reading posts on this site I am reluctant to get a roomette when i next decide to travel East. I do not fly so I would rather sit in coach and bring my own cache of food. It is a shame that the quality of service has fallen so much.
The current experience on the SW Chief should be little different than what you experienced in the past with traditional dining and Sightseer Lounge.
Flex is on the eastern connecting trains out of Chicago. Enduring one night of coach to avoid it, and the more expensive sleeper fares on those trains is a reasonable choice, but there is no reason to avoid the SW Chief.