There's a case that Leyland isn't making a horrible mistake by platooning Bosch and DYoung at the 5-spot: Both have more power than the alternatives, and it takes a lot of power to get Prince Fielder home from first (or second, for that matter). Batting a singles hitter fifth means you'll need the next hitter to get it done.
Still, he's not quite right. Assuming JICF for first 4 in the order, Dirks needs to hit fifth against right-handers the way he's going; he's sustained his OPS vs. right-handers long enough that he more than makes up for Young and Bosch's better power. And since Fielder doesn't always reach base anyway, Dirks is a more reliable bat than either Young or Bosch for getting the other guys home. Also, the R-L splits say that even though QB has cooled off, he's still a valuable down-the-lineup hitter vs. right-handers.
The good news is the Tigs face lots more right-handers and can be depended on to beat them pretty regularly. The bad news is this lineup is pretty hopeless vs. lefties. Even Cabrera has only two homers off LHP. And DYoung is by far the best option at 5 (and arguably at 4). Only Miggy and AJax are securely ahead of him (Omar, too, technically, but I think he helps the team more by facing fastballs in front of Cabrera and Fielder).
So: Vs. RHP
Jackson-Infante-Cabrera-Fielder-Dirks-Avila-Bosch-Peralta-Berry
vs. LHP
Jackson-Infante-Cabrera-Fielder-Young-Baker-Peralta-Laird-best available matchup, and prayer.