First off, there is only one handicapper being mentioned here, not the plural "handicappers" NJ claims. Reliable polling on the topic on a district-by-district basis has been sparse, so any assumptions on this hurting one over the other is nothing more than speculation at this point. Nate Silver, for one, would disagree. From what I have seen on the ground, and admittedly most of my more politically active friends are conservative to libertarian, the people are more upset about the wasted money, the debt, and the fact that the shutdown didn't really shut anything down-- all things that play into the conservatives' hands. People like Allen West and Mia Long who lost last time around would find far more favorable conditions in this environment, without the Obama coattails.
(As for the accuracy, I remember back in late 2012. I think most of us understood that the road to a Romney victory would have required him to win states that had not voted GOP in a presidential race for quite some time-- Wisconsin, Michigan, Pennsylvania-- to make up for the loss of places like Virginia and Ohio. While I might not have agreed to the extent Romney was an underdog, given that there was polling showing Romney up in those states before the election, Silver was not far off base saying Obama had the natural advantage, as much as he did not deserve it given his record.)
Second, I find it interesting that nobody has been talking about the Senate, which is where the real battle lies. Any anti-incumbent sentiment (and all the polling has shown it is strong) would work in the GOP's favor in that chamber. But let's not talk about THAT. That disrupts The Narrative.