They've got Green and Durant at the wings, why in the world would Walker have more opportunity there? At least here, if he stuck around, in a couple years he might be getting a lot of minutes. In OKC, he might be a career ten minute man.
Nevertheless, if I were OKC I would take that deal in a heart beat. Livingston is going to have to live off of experience in limited playing time to have any impact. His career now will be at best a consistent back-up player. At worst out of the league, or consistently on the IR.