At the time, it was necessary, because Stroman was in AA, and Hutch was recovering from Tommy John surgery, and Sanchez was still in A ball. Jays fans at the time didn't want to wait until 2014-2015 for those pitchers to come up. Casual fans don't have the patience.
BTW, Nicolino and Syndergaard aren't close to the majors this season, as neither is expected to reach the majors until 2015(Syndergaard) or later, in Nicolino's case(he's in AA still)
However, we should have kept Henderson Alvarez..although it's unknown how he'd do in the AL if he had stayed. FYI, Desclafani, who we also traded, did get to the majors, but with poor results.
Otherwise, you're right that we should have kept the guys we traded..