Both really. Warlock DoTs were pretty powerful back then and popping dark soul then going to town would rot a team down crazy fast. But yes it was also because we synergized well with resto and were pretty hard to kill.
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@brusalk
I accidentally made myself sound more inexperienced than I am. I do understand sp coefficients, stat weights, etc. I mainly needed clarification as to the reason of our scaling, be it secondary stats, the meta gem or trinkets. Thanks for the explanation though. As you can probably tell from my comments I simply haven't played this patch and as a result I didn't know what's been going on in PvE for destro.
So, according to simcraft under the BiS profile, these are the stat weights for our specs atm.
http://simulationcraft.org/530/Warlock.html
I gotta say man, it's not destro that needs to be brought up. It's affliction that needs to be brought down. If a spec has both haste and mastery at above 4, of course it will pull away. Destro is actually in a nice position where all three stats are decent.
Now, the obvious solution for blizzard would be just to buff the sp coefficients for destro. Will they do it? Who knows. You did mention earlier that making chaos bolt faster would further devalue haste, mainly cause of the gcd cap. Are haste levels at that point where we actually get gcd capped under BL? If yes, they really need to make immolate generate embers on every tick, at which point haste would gain value again.
On to your point about a proc, I can actually agree with your sentiment and perhaps a proc isn't the best solution.
I do like the idea of rapid fire destro, mainly because I like both PvP and PvE. In PvE, a slower CB isn't the end of the world, cause blizzard could make it hit as hard as they wanted to.
It does create problems in PvP though. There, it becomes a situation of either manage to get those casts off and blow something up, or you fail and as a result get very frustrated. With KJC not affecting CB anymore, destro needs to be a faster nuke spec or it will never be good in PvP again. Blizzard already felt pressured to nerf CB because people got scared seeing a huge skull fly at them and obliterate them. It doesn't matter how easy they are to stop, people hated it. Now with our mobility gone, we just won't be able to get those casts off. Hence my suggestion of a faster CB that costs less embers and does less damage. The spec would still play the same, with the difference being twice as many CBs during the burst phase. You'd still have fast nukes and controlled burst, just in smaller chunks.
I really don't see another way to make destro viable in PvP again. We either need mobility or speed. In 5.4 we'll have neither. I don't like adding procs either so I really only see this as a good option. Unless they added the other idea we've discussed, and make CB have an adjustable cast time.