A tough one to judge.
While Mo is a better shooter than Devin, that's about it. DEFENSIVELY, this is a downgrade at PG. Mo, at 6'1", will be helpless defending the likes of Derrick Rose, Deron Williams et al. Earl and Tinsley are poor defenders, although the effort is usually there. Devin at least had enough athleticism to contest. Remember, Mo was like only THIRD string on the Clippers until injuries got him more PT.
With that said, Marvin in theory should make us better overall offensively. He's got skills. And he is a good rebounder, which we need; he's actually taller than Millsap. ALSO, this gets Hayward to SG, which I think will help him improve his game. Not sure 'bout Marvin's D, but he at least has some size and athleticism.
We might see Hayward bring the ball up a lot more and getting us into the offense, which is not Mo's strength, but then it wasn't Devin's either. Gonna be interesting to see how this all pans out.
IMO, a gutsy move by KoC...