I like on/off number as a stat. In every metric the nba on/off advanced stats uses the Celtics are worse with Morris on the court than off the court.
In other words lineups with Morris, shoot worse, rebound worse, pass worse and turn the ball over more than lineups without Morris. Lineups with him in them have a worse defensive rating than lineups without him.
My eyes tell me the offense is worth because Morris kills ball movement, this leads to poorer shooting, and less assists. The worse defense doesn't really match the eye test because I think he's a pretty good on the ball defender, but maybe his poor rebounding at the 4 hurts defensive possessions.
I think Morris isn't good and the fact that Morris/Semi are our best small ball 4's really hurts our ability to play small.