Personally, I think competition under the WTF Rules is harder than self defense.
Apples and oranges.
I feel Olympic style sparring is more cardio demanding due the the continuous sparring. It requires more of the aerobic energy system (in my opinion) than does point sparring.
Point sparring is more demanding of the anaerobic energy system. More like a series of quick sprints (intervals) than a long distance run.
Both Olympic and point demand energy from both aerobic and anaerobic systems. Neither is exclusive. The difference is in percentages.
I'm not really sure how you are defining "harder" though. If you meant harder in terms of conditioning, then I've answered your point. On the other hand, if you meant harder in terms of difficulty... That's a tough one, because what is difficult for one person is easier for another.