I don't think Casey cares about defense anymore, just wants them to be an offensive team. Why else would he have Lou and GV on the floor together earlier lol.
They've gotten worse though, and it's not like they made a whole lot of changes in the off season. Lou Williams is a bad defensive player but they also added JJ.
All the advanced metrics rate JV pretty well. +/- is reliant on the rest of the line-up and opposition. I don't have the stats to back it up but I feel like JV hasn't been on the floor against subs very much this year, I could be wrong though.