Anytime you can make a deal to upgrade at a spot without losing majorly at another you do it. Plus in this case you lose NOTHING but a bit of depth. MJD will crush Greene's output, and you still have RB depth even with dealing 2RB for one.
Lookin at that squad after this deal you really shouldn't even any issues making a deep push this year, I mean hell in a .5ppr league you have three of the best RB in the league, and even if Mendy and MJD aren't top receiving options McCoy is a STUD in that category. When your talking about a runningback who rushed for 1000+ and with his reception total would have been TOP FIFTEEN the entire league in total receptions, damn. You have to do that deal and not look back.