I don't dislike Cesc or have an agenda against him because I'm not a Barcelona fan, however I said years back even before he was signed(reported that Barcelona were interested in him) it would be a massive mistake. Don't think anybody can really dispute that at the moment he's not been a success by a long shot.
Not only is he hurting the development of a more talented player in Thiago, trying to integrate him into Barcelona has caused you's problems the last two seasons. Okay you's will win the league this season, but I think you've been helped by Madrid at the start of the season and the ability to gather points late on earlier in the season.
Have no doubt the Cesc fans will come back and use stats as a reason for him having performed well, but are they really naive to use such things? His stats have been increased massively due to two games against poor teams in Deportivo and Mallorca. Cesc has not done enough to justify his price tag and the continued favoured treatment he received from both Pep and Tito.
This point that once he plays in midfield he will improve, doesn't wash with me, he's played poorly in that position many times. His best position is an attack midfield role with freedom to do what he wants, like at Arsenal, he will never get that at Barcelona because Messi plays in the space that Cesc used to have a free role in. His short passing, discipline and his style does not suit the Barcelona style and it's very evident, IMO.
Barcelona should cut their losses and sell him, you could still receive a fee of over £20 million easily, because frankly I can't see him being a success for you's. Same with Sanchez.