There are very very few flawless players. Castro's defense is no good, but still he is very young. Anyways if he doesnt cut it at ss they can always move him to a different position.
Clevenger will probably be getting plenty of starts, more depending on soto, till soto heats up or fails to, or gets traded.
As for barney sitting one day... guys get off days. You have to keep you bench players active.