I don't discount the change of scenery aspect, but they had the opportunity to let him ply his new swing in AAA for awhile. The reasons normally given, that they thought they had the position filled with Grossman, or that JD's minor league salary would be too high, don't really do a good job of exonerating them. If they had let him play at OKC and he still struggled, I doubt there would be as much criticism.
And I don't mean this as an indictment of the decision makers as anyone who makes a lot of these decisions will make mistakes, but it was clearly a mistake.