Log in on Winston after the patch and go try killing some random mobs in the Vale. If you can kill them, affliction will probably be fine for leveling. Don't let the opinion of one raiding-oriented player affect your judgement about a spec so much.
I followed your advice. The Vale Sha just melted away. The only issue I had as Affliction was realized that Malefic Curse (or whatever it was called) had gone away, and Drain Soul was now the universal filler. The only issue I had as a player is my frames UI mod (X-Perl) has not been updated for 6.0.x yet, so I couldn't see the absolute health of the mobs, only the relative lengths of health bars.
On the other hand, my better-geared Fistweaver (iLvl 560ish vs. Winston's 500ish) was sluggish compared to 5.x. I hadn't appreciated before how much haste affected ability cooldowns. I could still get a mob down, but it takes longer than it used to.