I guess that I am confused. Who are we discussing? Pablo? If so, yes, I do believe that benching him or whatever was the correct move. He simply is not prepared to play at an acceptable level.
I don't know about Castillo or even Swihart.
However, neither of those two are finished products and could use the time in AAA to get better while not hindering the Sox by playing sub-par ball every day in Boston.
You are correct that Swihart would likely be the #1 if Vasquez was not deemed ready and available to upgrade the position.
Castillo? I just do not know. He appears to be very athletic. But his baseball acumen is not sufficient ( apparently ) to warrant a a permanent starting gig on the Sox.