Under Brad Stevens, the Celtics never won a playoff series without Al Horford. In meaningful games, they lost convincingly. So it's fair to wonder if Horford, not Kyrie Irving, was the bigger loss for the team.
The truth, whether you want to hear it or not, is that we really don’t know about Brad Stevens right now, either. The coach of the Celtics has been smart, humble and even-keeled during his career here in Boston. What he has not been is tested.