It's on Morey because he bought into Harden, and it's on Morey because he actually decided not to go for it this year after Joel's injury (which is at least defensible). The only part that's not his fault is Harris. But it's also not Harris's fault the Sixers decided to use their Bird rights on him and he never really fit. Not sure how you can expect him to just magically become a star or even a third option when he was always changing positions and roles over the years and was always plainly what he is, a good player but not a star (and any team that had him as a star is not going to be a good team).
The roster Morey started out with (after trading Harden) wasn't terrible. Injuries (not Joel's) did hurt them there.
Obviously Morey isn't going anywhere, and Joel probably isn't either. Forcing his way out probably wouldn't go any better than the Sixers deciding to move on from him.
And Harden may yet have the last laugh. Everything Dice has said about Joel was true of Harden last year... but it was a better team. Too bad we didn't get to see Nurse coach it.