I have looked and his stats do not drop as drastically in second half of season in all competitions over the past few years.
They do drop and part of that in not one of those seasons was his position in the team kept consistent before and after xmas.
I am sure he is second only to Messi in stats in the second half of the season the past three years although would need to double check.
It is almost as if he would be appreciated more if his stats were better than average in the first and second half of season. He would get more praise for that than being exceptional stats in first half and still very good stats in second.
The stats that I've provided do show his drop of form and it is rather drastic. His impressive stats at the end of each of the seasons is largely due to his fantastic first halves. Nobody has claimed anything else. The only thing I'm criticising is that part. As for the position changes, it may have had some effect, but he still had some great games as a false nine.
I agree on the last part of your post. The thing is that had he retained some of his autumn form where he was scoring and assisting for the fun of it, we may have won the league. Of course, we can't pin it all on him since it requires a team effort to win the league, but it's not unfair to have expected more from Cesc during the spring. But to be fair to him, he wasn't the only player whose form dropped - most of the players did, so it's not entirely his own fault, but he still has a part of it.
I'm not a Cesc hater, if that's what the rest of you think, I'm only criticising where it's due.