I think roster construction (i.e. Hosmer/Mervis both being LHH) is a as big a factor as any for me. Hosmer doesn't provide a level of defense that appears to be game changing a la Rizzo from the eye test thus far and even if it's a modest increase in offensive output, I have to think that just getting away from all the damn ground balls he hits will have a net positive effect. Long story short, Hosmer is a minimal sunk cost, Mervis is probably better already and hits less rally killing GBs, so bring him up and let's see what we have.