I'm not necessarily saying we have to have one or the other. What I'm saying is that right now, Nardo is still an unknown variable. He took over a crappy defense, and that defense hasn't improved much. However, there have been moments of improvement. For example, much of the first half of this week and the first half of last week. The defense played really well.
Ultimately, we can't fix box problems simultaneously. We need to address the glaringly obvious problem first, which is that Dunn is a God-awful OC. While we're doing that, we can continue to evaluate Nardo and see what he can or can't do. He deserves at least a 2nd full season before people start casting him off. However, it's tough to be great on defense when your offense is this pathetic.