One of the things you will (or maybe won't) learn about baseball is that there are numbers everywhere. The easy numbers to pick up on, and the ones that were historically given the most credence, do not tell the whole story.
When you look at the last Sanchez start in a vacuum it looks good, 7 innings, 0 runs allowed and a team win! All super great things. But those, in and of themselves, are not repeatable skills that show what he is likely to do going forward. As it stands now, he walks far too many batters (the biggest criticism that even his most ardent supporters will cop to), and he doesn't generate a lot of swinging strikes (a good predictor of future success). If you look at his numbers in the minor leagues, this has been a problem since he was drafted and hasn't shown signs of improvement.
I'm not in the "he sucks, trade him for whatever you can get" camp, I am, however, in the "he needs a lot of work, and he may never figure it out" camp. He has two things going for him, he is 22 years old and has time to work on his problems, and he can throw the ball really, really hard. Hopefully he can figure it out (tercet is probably the only one here who is actively wishing that he fails, but I think that's because he's jealous that both he and Sanchez are 7'3" and 118bs and only one of them got a $775,000 signing bonus...)