Enderman spawing in soulsand valleys is very frequent

1. step on a soulsand valley (sim. distance to 6, hard difficulty)
2. do /kill @e
3. observe the ghasts, skeletons and enedermans

you will see that more endermans spawn than skeletons and ghasts

ghasts and skeletons should be spawing more than the enderman in the valleys

 

has been resolved!