OK, let's have a Sanchez debate, having said that however I would focus not only on Sanchez, but on all non-massia products (transfers), say Afellay, Song, Villa, Cesc and Ibra, just to name a few. All of these players proved themselves to be a key factor on another team or league. So let's just make one thing clear, they are ALL great players. What they can do for Barca does not only depend on them, it mainly depends on coaching, tactics and strategy. I often hear comments about so and so being out of position, well, who's fault exactly this is? player's? or a coach's?
Let's go back to our "bad" boy Sanchez, don't you think if his coach told him to focus more on better plays, other than useless dribbles, ball wasting and diving, he would actually be more productive? he has speed and technique, he just does not use it right. If something doesn't work, cats now that well, don't repeat it, so if we assume Sanchez is not smart enough to figure this out by himself, shouldn't this be a coach's job to fix it?
Look at this from another perspective, sure Afellay was a bargain, but he is very good player, many (if not all) here really like him, but what did he do for Barca during his term? one fabulous assist, few insignificant goals and that's it. Could he have done more? of course he could have, is that his fault or coaching? players are told what to do on the pitch one way or another so please, don't just blame Sanchez, Song or any other player unless they make blatant mistake
Many also believe Cesc is not performing, how may would actually say he is a bad player? not many I bet