My experience is that AI agents write 20-33% more code than I would for a given feature set, mostly because they are worse at remembering what utility functions already exist and less likely to merge similar functions into more generic ones. They generate that code 2-10 times faster than I could. Defect density is harder to compare: I probably generate more "dumb" defects due to oversight or missing unit tests, but fewer defects that violate domain rules or architectural objectives.