I know that's a popular narrative, but I think it's impossible to quantify the effect of his holdout on his play. What we do know, though, is he has been a slow starter every year of his NHL career. Take out the hat-trick in his debut and he was put on the 4th line for a while early in his rookie season. Through nine games in 11/12 he had 0G 2A. Last year's early season slump was highlighted in this embarrassing thread:
http://hfboards.mandatory.com/showthread.php?t=1332525
I don't know if four seasons is a big enough sample to say he's a slow-starter, so it could just be noise instead of a signal. Either way, he, like most other Rangers, needs to pick it up.