If that's why you think it's no longer the go to spec then you're horribly misinformed.
It's losing its viablity because the other specs needed buffs and they got them.
Plain and simple.
Even still, it didn't really lose its "viablity". If nothing else changes right now we're looking at all three specs excelling on different bosses in heroic progression. This may very well be the best job Blizzard has ever done balancing all three specs.