Chick still does some good work, so "downhill spiral" might be a bit rash, but yeah, he'd definitely done better if Don Schlitten had been producing him all these years, I do believe, if for no reason than that there would be more exclamation marks.
Then again, Schlitten's put all his money in the Mathuey Amalric basket, and who can blame him? Producing movies is a much more sure investment than is producing jazz records, especially when it's your brother.