I don't know that there's a consensus on what the limit really is. Semaglutide is good for about 15%, tirzepatide about 20%, and retatrutide about 25%. Some people don't get that much, some people get a lot more. Personally, tirzepatide got me just over 35%. I never got anywhere near max dose, either, I am what is colloquially referred to as a super responder.

As you lose weight, your body needs fewer calories to run. That “needed amount” keeps dropping with your size, until it eventually equals what you’re eating on the medication. At that point you’re no longer in a deficit, so weight loss slows or stops.