There's really not much to discuss here. Cats with food-related medical conditions should be fed the veterinarian-recommended food, yes, even those containing by-products. If you find a certain premium food that you think might be better, always consult with your veterinarian before switching.
I've had my own experiences with these issues in the past and present. When Shannon, my first GuideCat, was in his final months of life, he suffered from FIV and CRF, and became very anorexic (also complicated by gum and mouth problems.) I fed him a mixture of Hills A/D, baby food meat, supplemented with Nutrical; and finally resorted to syringe feeding this "soup."

More recently, in his last months, Bubba was able and willing to eat and keep down only Friskies canned food, so Friskies it was. With anorexic cats, the important thing is to get them to eat anything they will eat. They always can be weaned off the lesser-quality foods when their appetites improve.

• "I also have a very picky cat who has rejected most of the best foods on your list and who is also periodically anorexic, so there are definite compromises needed that way."
  Pat (raleigh04)
• "I also had one rescue cat who refused all other food besides human tuna and Meow Mix. No matter what I tried, she would starve herself (and she made herself very ill) until I gave in and gave her one of those two. She was an ancient cat I rescued from euthanasia at the kill shelter, and she was probably raised on that diet for 15 or 20 yrs before I got her. I couldn't change that, so I had to accept it. She died happy and old, eating her Meow Mix with occasional tuna as a treat."
  Kelly (HOSTKel)

Limited Availability of Premium-Quality Foods
People in the U.S., Canada, and larger metropolitan areas elsewhere in the world are fortunate, because nutritionally good foods are easy to find.

However, in other areas it is sometimes difficult to find commercial cat foods, let alone the premium brands.

The Adoption Issue

• "I don't think people would ever get the idea not to adopt if they couldn't feed top-quality food. I too agree that a cat in a home eating sub-par food is better than a homeless kitty."
  Catherine (CatherineLuvsKitties)
• "Those who do the research and look into the various aspects of getting a cat before actually adopting one might be deterred if they either couldn't afford that expensive of a diet or couldn't find quality food in their area. I don't think that would happen very often, but you never know..."
  Sarah {Sarahava}
• "I would have been one of those people who would not have adopted a cat if I thought I could not do right by them. I would have felt bad to know that I was taking on responsibility for this animal, when I knew that I couldn't do what was best for them all along, and I would not have adopted them, even though we did have all the other essentials of a good home."
  CINDERS2
• "If a person can't afford $9-12 a month for quality food, are they going to be able to afford shots? Routine vet visits? Dental care? Emergency vet care? Is kitty going to be put down at the first sign of chronic illness? Is kitty even going to be diagnosed or will the tests be too expensive?"
  HOSTDES
• "Since Fred has allergies he has to be on special food. Since he has been with us I have actually been able to get him off IVD and onto Sensible Choice & Chicken Soup (Thanks to your articles!). But whoever applied to adopt them would know right off the bat that the food was part of the deal. They would have to be willing to feed them that or no adoption."
  Jenn (JENNCOULL)

False Economy

• "None of your nutrition articles advocating top quality foods are going to stop those who have read your articles and also want to adopt cats from doing so just because they might not be able to afford your "top picks" on a regular basis. Your articles have always been the "best" in cat care to which I refer many people, and it would be terrible to read your "Best of the Worst" foods articles. If you did such an article, then you ought to have disclaimers about how those foods will keep a cat alive, but not in thriving health and may, in fact, contribute to health problems developing on down the line with continued use, especially the dry foods with high grain contents."
  Galen's Granny

These issues certainly do present a quandry for writers like myself, who counsel people on food choices for their cats. I have no "magic bullet" that can resolve all these concerns. The best I can advise is to buy the best cat foods you can afford, supplement them with raw chicken (or lightly braised deboned chicken thighs), and compromise in other areas.
It's worth repeating that in the "olden days," before premium foods were introduced, many cats lived long, healthy lives on diets of "grocery store" cat food, my own included. Although most of us would not willingly return to those habits, there are times when compromises are necessary.