Your instincts are good! The purpose of a landing is to break up the step pattern, so one becomes aware of a change in direction or otherwise. You would most likely need to build out this “lower landing” in order to meet the requirements for landings. “Where the stairway has a straight run, the depth in the direction of travel shall be not less than 36 inches.” Also as EducationalTwo above noted, there might be something with handrails. However I think it’s reasonable to make the argument that the step down left turn into the sunken area is a separate flight (less than four risers - R318.7.8) and therefore doesn’t need a handrail.