David really needs to be evaluated on his own terms, and not compared to Mark. And for sure not viewed as an inferior version of Mark. I feel David sounds more like artists such as Springsteen, Dylan, (late career) Cooder, John Hiatt, etc, i.e. artists with a less elaborate musical expression. Just now I'm listening to his Heartlands album. First of all it sounds great, much better than I remembered. And even though I'm not a fan of David's voice (it's growing on me), he sings with lots of emotion and presence. Something which I find sorely missing in Mark's recent music.
I am actually surprised by myself. I had never thought I'd come to enjoy David's music.