Here is what i think everyone is saying in regards to criticism to Sanchez..... He has a good fastball which does over match hitters at times, he can be a good starter if he does the following......
Reign in his control, that was a major problem last year he walk over 4/9ip which is terrible and people need/should realize this so yes he needs to get his control issues under control.
Develop his curve is next and develop a 3rd pitch. IF he does not have another 2 solid pitches in his repertoire he his not going to last long in ball games. Last year he threw the Fastball over 80% of the time which is fine when he is in the pen but as a starter you have to rely on other pitches or your not going to make it out of the 5th or 6th that often because hitters in this league will just zero in on the fastball and leave the off speed stuff which he can't throw for strikes with regularity.
Nobody is saying he can't be good. They are saying that he has areas that need to be improved on before he can bee good. Its easy to look at spring stats and say he is good when at this time of the year pitchers are generally ahead of hitters in terms of being ready for the season.