The D-Backs need MLB ready young pitchers. Gee and Familia fit that bill. Don't think of it as prospects for prospects think of it more as trading from positions of strength to fill a need. I don't see why the Diamondbacks wouldn't make that trade. They get a late inning reliever in Parnell. A potential number 5 starter in Familia and a decent outfield prospect in Puello. They already have a strong outfield and we are desperate for outfielders.
And anyways Parnell would be the main player the D-Back would be getting in that scenario and he is not a prospect.