Well, the boat designers can elaborate, but - I'll give two answers to the previous post. The first answer is best explained by Bethwaite High performance sailing, section 16.3, and the figure by the same number. It essentially refutes the "just hike harder, and make up for it downwind". Essentially that while you can "hike harder" and add perhaps a few percent righting moment compared with "not hiking harder" (whatever that means), you are going to need to depower the lift of the sail (heeling moment), while you can do little to proportionally reduce the drag (once you have flattened, etc). Sure, there's an overlap range, but that's why 18s, etc have multiple rigs - simply because it is faster over a range of wind conditions. Note that in these cases (at least if you believe Bethwaite), , shorting the mast is well worth it (vs a sail that does not go up to the top).
Perhaps you really were trying to answer a different question, however. When 18s compete, there is essentially one class, and it is assumed participants will own all the rigs and pick per their preference. So, if you may, there would (theoretically) one dpn number assigned for the combination of the 3 rigs. This is not how mere mortals do it, however. While I may own a laser and a radial rig, the laser class does not consider that one class. So - in the case of the aeros, and eventually D0s, you are correct that splits the class.
And that is a valid concern, especially for a class starting out. But.. it is a double edge sword. With the current mix of boats, I think it is pretty clear that if I were a 65 kg woman or youth, one of the two smaller Aero rigs would look like a better fit for me. But.. if I were a 80 kg guy, I the 8 m2 sail the D0 has looks like it is a nice sweet spot, especially if I didn't live in a windy venue. Sure, people can sail on both sides, but.. this is a game of sweet spots. So - as I see it, let's not criticize the competing classes, just realize that each is potentially going to work best in different target audiences. Also remember that not all people buying boats are competitive laser sailors looking for something "just like the laser, but with the stupid things fixed". This forum (and the Aero forum, for that matter) have LOTS of selection bias going on, but I would posit that especially for the aero, there is a lot of target customer base (less serious racers, women, small guys, youth) that does not hang out on forums for a pasttime. So I guess this is my plea to forget spending lots of emotion about what the aero is doing, and concentrate on how the D0 fits you and your club on a case-by-case basis.