I think it speaks a lot to DD's use - throughout most of the game I would think he has a positive impact on the offense, but in the 4th he absolutely kills it due to bad playcalling and excessive iso's (not necessarily all on him, obviously). He does still have an overall positive impact offensively, which is good to see, and he's improved drastically defensively this year compared to similar stats in previous years. Anything positive at all is "above average", so this looks pretty good on him, I think.
Players like Fields and Amir who do so many little things will always look great on these team-based stats, but you still need guys like DD, Lowry, etc to make the wheels turn, and if they can do so while still posting solid (or superstar, in Lowry's case) numbers in team-oriented stats, that's great news.
I'm doing a quick and simple wins analysis with these plus-minus numbers (I hate ESPN's WARP) to see how it shakes out compared to stuff like WS and WP.