I think I'm just lucky.

I did no real research. It went like this:

Roommate's girlfriend moves in with her cat.

My cat develops skin problems, suspect fleas.

Treat for fleas, not better, cat also gets fat, and starts this weird gnashing when scratched. No idea that the gnashing and skin problems are related. Think the gnashing is cute.

Notice that cat's food is different (I don't do the shopping). Ask about it. Get told it's what his girlfriend's cat eats and it's super cheap, plus she (the cat) really seems to like it.

Remember a dog I had decades ago had skin problems and needed expensive prescription dog food.

Briefly google "good cat food", points to fancy feast as at least not terrible.

Acquire fancy feast.

Cat acquires health.

I DID plan on moving to a real premium cat food but then it seemed unnecessary after the dramatic improvement.