So at 50%, someone who uses AI to get 100% of the homework grade will earn a D (sometimes passing) if they can get at least a 20% on your quizzes, and a C (always passing) if they get at least a 40%. Did you make your exam so difficult that students who truly didn't learn the material earn less than 20-40%? Because if it was, say, multiple choice questions with four possible answers, then you can expect them to earn at least 25% just by chance.
My quizzes are written responses, psuedocode and annotating code.