This is a good move and shows we're still trying to improve the squad defensively. We got good value in this trade and definitely filled a need, and after the recent moves/rumors this is a clear positive.
However, will he be our starting SF or not? That's a big question as unlike I others, I disagree we need a defensive, role playing SF who's not much of an offensive threat as our starting SF. That's what we needed when discussing a possible Reke/MLM backcourt. But now that we have Vasquez/MLM, we need a SF who can create for himself and others, a 2nd 1v1 scoring threat outside of Cuz. If Mbah is our starting SF, we don't have anyone at the 1, 2 or 3 who can create on their own and that's a problem. If Mbah is a backup SF to a YTD SF, it's a great pickup and adds depth.
But we need the 2nd 1v1 threat from the perimeter which we had and haven't replaced. A lockdown defender at SF who can get you 10pts is great, if it's next to two 1v1 players who can create off the iso. But that SF next to a role playing PG and a SG who can't create his own shot is less valuable.
Until we get that 2nd 1v1 threat we're basically relying on Cuz to turn into Dirk and put all role players on his back. And Dirk as great as he is, was in the league for over a decade until he was able to do that. Or imagine Duncan without Parker's penetration and 1v1 ability, and without Manu's ability off the dribble. In that scenario, a great role player like a Leonard is considerably less valuable.