I think Mayer shows a lot more plate presence and recognition than Campbell does. I'm not yelling at anybody, nor for them. Campbell isn't just in a slump, he is currently seriously flawed at the plate.
Mayer also may not be ready but let's give him as many PA's as Campbell to see if he can adjust.
Rafaela is a good example of someone who does not adjust but is posting just enough numbers to back up his flyball saving defense . Doesn't make him a good player, just affordable in a 9 man lineup.
Trouble is, the team should not have to afford 3 of those guys at once.