Pulling from this blog post, How to Balance Unstructured Group & Solo Rides with Your Training Plan | TrainerRoad Blog , the implication seems to be that “easy” workouts include all your edurance stuff while “moderate” is more tempo or sweet spot (or harder), and ‘hard/very hard/all out’ is anything above that.
I think that helps as another layer for reference on rating workouts in the sense that if I’m doing an endurance ride, it should probably be of a noteworthy difficulty (ie, feel like tempo or sweet spot) for me to rate it ‘moderate’. Equally, the Vo2 and Anaerobic stuff should default to ‘Hard’ or more.