Still not enough data.
As you say the weather was not the same so we do not know how Evans would do in the same weather conditions. Evans was not deterred on the mud stage of the 2010 Giro. Okay a different surface but everything about his background indicates bad conditions would suit him well. The dry conditions almost certainly helped Evans rivals including, Schleck, Menchov and even Contador in 2010.
The whole circumstances of the way Nibali and Evans came to the cobble stage were completely different. Evans had raced a very hard Giro and no one thought he actually would be able to be anywhere near his best because of this, perhaps in his heart even Evans didn't believe he could back up. Evans needed to conserve all the energy he could. So attacking the lead group would have been completely against what he was trying to do, he made time on everyone expect Schleck without having to do anything spectacular. His tactics worked well, he got into yellow, however having crashed meant he had no hope of being competitive, if he ever had any hope.
Nibali on the other hand came into the race completely fresh and knew he was up against two excellent climbers, perhaps a bit better climbers than him, so taking time in other stages was vital to his bid. He also had a teammate with him the whole time, having Cancellara certainly helped Schleck in 2010 and having Fuglsang also helped Nibali.