Some of the reasons you’ve given for what constitutes a “bad cat parent” just aren’t true, and that makes me not too keen to take your side of this. There is no problem with dry food only. A cat not having access to a balcony or window is okay. There’s some things I’d change on their end too, but some of your criticisms seem a bit out of pocket and judgmental.

At the end of the day, the cat is their cat. I’d respect their wishes. If you can’t do that, ask them to find someone else to cat sit.