It is possible to make a list using only greater daemons that not terrible? Here is my attempt at it:
++ Supreme Command Detachment (Chaos - Daemons) [63 PL, 1,000pts] ++
+ HQ +
Great Unclean One [17 PL, 250pts]: Bilesword, Fleshy Abundance, Nurgle's Rot, Nurglings, Plague flail, Smite
Keeper of Secrets [11 PL, 210pts]: Hysterical Frenzy, Living whip, Smite, Snapping claws, Symphony of Pain, The Forbidden Gem, Witstealer sword
Lord of Change [17 PL, 250pts]: Born of Sorcery, Gaze of Fate, Infernal Gateway, Smite, Staff of Tzeentch, Treason of Tzeentch, Warlord
Skarbrand [18 PL, 290pts]: Bellow of endless fury, Slaughter and Carnage
I would use the exalted greater daemon stratagem on each one (except Skarbrand, he's a named character), choosing to roll two dice instead of picking one since none of the exalted daemon traits look especially bad from what I have seen. That would give this army 3 CP to play around with at the start (based on 9th edition rules), so it's not as starved for CP as it would be in 8th edition, though I would still use Gaze of Fate to avoid spending 1CP on the reroll strat.
The only choice I am questioning in this list is taking Skarbrand, since he is rather slow and expensive. But he does the one thing all bloodthirsters should do but don't, not have degrading attacks, and it's not like there is anything else I would spend the points on. Besides, he has a very good chance of killing a dominus knight in one turn, unlike a normal bloodthirster.
So would this list be competitive and would it be fun to play against? Can you make a better greater daemon only list?
Obviously this assumes that this is not an objective-based game, or maybe that there is only one objective.