When the engine is running at a idle, the prop is braking the plane and also is blocking the airflow to the elevator somewhat. This decreases elevator control and makes it harder to land. This effect is greatest with large diameter props with a low pitch. I have a plane that does not land well at all unless I remember to give the engine about 1/4 to 1/3 throttle before touching down. When it is dead, the stationary prop does not block airflow to the elevator and perfect landings are a breeze.
Yes, they really are easier to land with the engine dead, it's not just your imagination.