I play a Demo Lock, so I will comment on yours. Does he know what a Doom guard is? It would increase his dps if he pops it, since ya'll aren't getting to sub 20% have him pop it about 5 seconds into the fight or when ya'll Hero. He also should be using a Felguard with Grim of Service or if he can't handle the active he should at least use Grim of Sup and use a Wrathguard. Link to our kill
http://www.worldoflogs.com/reports/p...?s=5085&e=5651. I have Grim of Service and my pet does 3.61% and the Additional Felguard summoned does .82%, and that is with controlled usage of my extra pet, not using it on cd, since this fight is all about control of adds.
Not sure why but he only has a 70% uptime of Molten Core procs, but he should use Soulfire on all MC procs, even when in Demon form. Have him look at the guides on Icy Veins or Noxxic. Much more information there, although the do conflict at times.
He has the UVLS so should be dotting Doom every time it procs.
He does have good Metamorphosis uptime.
He does not seem to be using Hellfire on the adds phase, which would be a benefit. (or Immolation Aura if he goes into Meta form).
I can't see his armory so can't get more specific on that sorry. Us here, and you are EU. but hope I have helped some at least. Good Luck!