Ignoring the fact that Fernandez was a generational talent, he threw 135 innings in 2012 with amazing numbers, and then got called up in 2013.
Osuna threw 109 innings in 2012, 2013, and 2014 combined, and had TJ surgery.
There was nothing indicating that he was worthy of a call up. AA got desperate because he had no money left to pay for a reliever, and he was willing to destroy the development of two of his prospects to fill those spots. I'm fine with how Osuna turned out since there are questions about his durability, but he should have been in the minors being stretched out. Or at least call him up to the bigs as a reliever after he's had a starter's workload in the minors, so that converting him back down the road could have been realistic.
Osuna probably had a greater chance of turning out like Castro than he did turning into what he became. That's a credit to his talent more than anything else that he was able to be this good this soon.