I guess he was actually plannend in as a true CM, but prolly Pep sees a lack of physical strength, awareness and marking to play that role defensively. You also cant really say that he got the passing in barcelona quite right already - bad timing not rarely leading to offsides. Maybe its b/c the passing in arsenal was quite different, much more straight forward and less diagonal and back passes.
Just dunno if it makes real sense to keep him for another season. I actually quite like Hleb as a player, but its a risk. If he still wont catch up he gets frustrated in his 2nd year which might lead to some conflicts hurting the teams atmosphere. If you want to avoid risks you let him go ... there should be players available of similar quality, but w/out his negative backround of the last, depressing season.