We lost 12% base damage to most of our ability's, this resulted in a few hundred damage on average being lost on each cast.
In return we gain 15% haste 80% of the time. A massive buff by any stretch of the imagination, the problem? Any warlock who isn't bad has been stacking haste out of they're ass leading to close to hard capped values. 15% haste when most of your spells are already hard capped doesn't actually do much.
This strongly leads me to believe that while haste is still important, we should perhaps consider trading some in for mastery/crit. I would suggest (of the top of my head, no maths to support it, just as a starting point) that a number closer to 25% haste would be a better goal to aim for. This would be the roughly 40% that leads to haste capping now, minus the 15% we get from improved soul fire.