I've now seen some analyst reports defending INCY, and they make some reasonable points.
Key seems to be that this trial had a wide dosage variation - some doses that were too low and some that were too high. So you would get discontinuations for both efficacy and for tox. Those discontinuations in turn would drive no improvement in OS. Also, the rebound effects claimed here do not seem to have been repeated in other trials for whatever reason.
So I'm starting to wonder if the weakness was an overreaction.