Exactly! When Matilda isn't a treat eater, but she does love more canned
food than she needs and would love to go out "after hours." When she starts
her whining, I say to her in a louder than normal voice "no, now shut up!"
She will snort at me rather indignantly but then will either eat the food
that's there for her if she's hungry, or go to her room is she's been
refused going out.

Judy & Matilda

For my cats, a treat is an addition to a whole meal. I count their treats
in when figuring the days total. For example: 2 of my 3 cats get daily
medication. After meds, they get a treat. For one, it is a few chunks of
cooked white meat chicken. For the other, it is either some of the same
chicken, or two days a week it is raw chicken liver. They have learned
that treat means treat. Not part of a meal, not a whole meal. They
associate their meds with said treat. I even call them to the kitchen by
saying "Medicine time" and they probably think "treat". My third cat who
doesn't get meds gets a few pieces of Wysong Cat Treats when the others
get their treats because the others do and it wouldn't be fair. (she
doesn't like meat, or raw liver.. or canned cat food for that matter).

For OP, I agree with GovtLawyer in that a treat shouldn't be enough to
fill up the tummy, but be a "taste treat".  Better yet, something to look
forward to when they do something without hassle, such as getting meds.