It was a minor trade for both teams with the Kings reportedly set to waive both players to get under the luxury tax. Acy is nothing special, smallish if you play him at the 4 and not a skilled SF, yeah he might be a high energy guy but he has to be to make up for what he lacks. Used to think Outlaw was a stud when he was in Portland but like you say he's been a bum the last few years but he has more potential to be Melo's backup at SF than Acy imo.
I think the Knicks did the deal to balance the roster getting 2 guys to possibly back up Melo rather than depending on Cleanthony alone to be Melo's backup. There were rumors that the Knicks were willing to give up Prigoni to get rid of Ellington which made no sense and I'm glad it didn't happen.