It's not "unviable". The nature of many of this tiers fights (with a lot of room to spread your dots) will continue to favour fire, as any mage who raids high-end would realize. This has also been the conclusion of our fire mage, who, previously, was impossible to compete with due to the nature of the fire spec on the majority of fights, and has now simply been brought back in line. Simcraft doesn't tell you that. Purely singletarget, well-played differently specced mages will undoubtfully outdo fire mages, but that does not mean fire mages are 'unviable'.
No offense, but generally people who say stuff like that really have no idea. Use simcraft to optimize your own results on each fight, not to "see where in the list my class/spec sits and therefore I'm shit". Nerfs don't happen just to piss you off, there's often a genuine reason and though the fire mage nerfs were sweeping, they were necessary and you know it.
If mage wants to "spread dots" then he/she should go arcane for mastery boosted NT which is lot better than anything fire can do. Cleave fights on the other hand are surely still fire specs strong side.
fire mages sits as last dps spec in the game in single target and real real bad in aoe, the only not so bad its on cleave for 2 or 3 targets.
fire loss on heavy mov and bad rng takes this spec into real garbage when you raid 25 heroic.
lets hope blizz will fix this for all the fire lovers.