JBJ
I'd have a greater understanding of having JBJ play every day at AAA if Rusney looked remotely decent at the plate or in the field. However, he doesn't. There are 107 games left in the season over 18 weeks. That's about 6 games per week. For the sake of argument, lets say that Rusney gets 4 starts per week and JBJ gets 3-4, spelling Mookie CF and occasionally moving into the OF to give Hanley a day off in LF. That gives JBJ about 250 PAs over the remaining 2/3 of a season. That's plenty of regular playing time and it doesn't even account for the fact that he may outplay Rusney over that period of time and obtain more playing time. If Rusney figures out how to play and/or JBJ sucks and it doesn't work out, then they can send JBJ back down and find a guy like De Aza at a later date.
Sure, there is the argument that they're not paying Rusney $10/per to be a bit player. That doesn't hold water for me because they were paying him that to start in AAA to give Shane playing time. IIt's just that at this time, this team needs performance far more than it needs to play contracts. I'd much rather see JBJ get about 100 fewer PAs over the rest of 2015 and the Sox put a better team on the field than JBJ sit in Pawtucket to collect those 100 PAs and De Aza get run for the next couple months (or until injury or further ineffectiveness forces the Sox to promote JBJ).
Brentz
This is more of a secondary issue than JBJ. I understand the Sox don't need another RHH OF. However, what they do need is another hitter that can hit LHP. To do this they have to spell Sandoval or Ortiz regularly against LHP. As I said, I don't think there should be another game this season when both of these guys play against LHP. To do this, they need to play Hanley in LF or 3B or find a RHH that can play LF and 3B that can come off the bench. Brentz at least gives them the ability to build a better lineup against LHP. He'd also only be a short term solution until Shane gets healthy.
Bottom Line
They can't get much worse. They need to field a better and more competitive team on a nightly basis, particularly against LHP. At this point, I'd rather them fail by being creative than continue to fail by being conservative. They may only be 5.5 games out but with this type of play, that's insurmountable. Considering these circumstances, the 40-man roster, and the acquisition cost, I just don't understand De Aza. If they were in a different situation, I'd get it. In the situation they are in, they should be trying to put together the best 25-man roster and lineup they can.