I get the impression from most posters that 3.3.x Destruction was the best Destruction has been in terms of rotation, it was a little underpowered thanks to PvP capping it's burst, and that did need fixing. The problem was however 'fixed' in too many ways: Player health was increased dramatically, Dark Intent was introduced to add ramp up and cap burst, DoTs were allowed to Crit putting more emphasis on them and adding Corruption to the rotation, and of course Improved Soul Fire was implemented to further increase ramp up. DI and ISF were, in my opinion at least, unnecessary additions; DI added a cap to output based on raid composition, and ISF is just a clunky mechanic; but either way, the sum result of all these additions hurt the playstyle for many in PvE, and limited the spec substantially in PvP. Having only 2 out of those four mechanics would have kept a streamlined spec, and maintained PvP viability.
For Demonology, again, once ISF had been moved out of reach was in a great place. Yes there were, and still is the issue of Mastery snapshotting, too big a see-saw of output between Meta and non-Meta. Pet balance could be in a better place with regards to affording the spec utility. But overall, the rotation isn't overly complicated - again it's just damage source management, not really resource; perhaps Shadowflame could go as a single target spell to eliminate the 'melee range' issues and drop a button. As it happens, Immolation Aura being combined with Hellfire, and it's high Fury cost, and the Fury system itself go some way towards 'fixing' the melee issue, and damage see-saw. Pet normalisation sorts the utility issue. So there are definitely positives to look at with what we're looking at so far. Again though, I think they're going too far to fix a perceived problem with an 'overly complex' rotation by removing Molten Core and Immolate.
Affliction, Blizzard said themselves they like as it is right now. Even going so far as regarding it as one of the most polished specs in game; I agree with that sentiment. Again, there are issues, particularly with Shadow Embrace that could be looked at since it is a burden other DoT specs needn't concern themselves with and perform better as a result, but that's about all there is. It's also our one spec which at present has some semblance of resource management through it's high mana usage. Again, that's fine, the rotation isn't hard and the resource management isn't either. What they seem to be doing here again though, is trimming back on spells when there is no reason to trim back other than that someone who doesn't play the class has this lingering perception from TBC/Vanilla that Affliction is overcomplicated.
The real problem, is that Blizzard have done nothing to reinforce those directions for each spec but instead opted to change them, or at least, try fix one issue from too many angles at once creating a perception of it and creating more problems in the process.