Fair, those are good points.
Luke is just a weird fit as a player. He's a great offensive player but tough to align on defense. IC has a front page article right now showing our efficiency margin was +17.3 points per 100 possessions when Luke played the 5, but only +1.3 points with Luke at the 4. Attribute some of that to Cam, but I think Luke is a matchup nightmare for opposing 5s and his spacing made our offense devastating (Luke's personal scoring and efficiency numbers were way up at the 5 spot as well, and this is over 400 minutes).
So I think we need to accept defense is going to be a good rather than great with Luke in there (Manley isn't great yet defensively either). I guess that means Seventh's defense is at a premium, but perhaps Coby can play with Kenny/Nas and one of them can matchup with the other team's primary initiator? All but the very best teams have one guard who's not a big offensive threat, though it is asking a ton of Coby to learn our system, point guard duties, and defending in 6 months.