I think we need some data on this ULW/LW/MW/HW/O Endurance issue, to bring things into perspective. This isn't perfect data, but it might give you an idea of the breakdown of riders. Below is the best I have access to, the number of riders who have scored points this season in each of these 5 races:

Open Endurance: 30
Heavyweight End: 27
Middleweight End: 39
Lightweight End: 12
Ultra Lightweight: 23

Looking at this, it looks like there are more Middleweight riders than Lightweight and Ultralightweight combined.