You have your schedules mixed up. All controlled substances have a potential for abuse. Schedule IV drugs only have a 'low' potential for abuse 'relative to the drugs or other substances in schedule III', not low overall. You could argue that it should be schedule III, but all controlled substances, regardless of their schedule, are more tightly controlled than any other unscheduled prescription-only drug.

Omeprazole is not a controlled substance and is OTC in the United States.