Let's put it this way: if the US did not have any naval AEW capabilities and had to design a new solution from scratch in 2016, do you really think the result would look like E-2D?
And yes I am talking about having the radar crew aboard the carrier, not having the unmanned platform(s) function autonomously, although obviously there would have to be some initial on-board data processing to reduce required transmission rates.
Apples and oranges. First off if the US did not have any naval AEW capabilities would also imply that the US has no or extremely limited aircraft carriers.
If China on the other hand has been flying AEW for 50 yrs and driving super carriers for even longer than I would assume the US would at least replicate some Chinese designs.
Your argument is only valid if there are NO naval AEW aircraft flying in this world at all in which case then yes they would have to design things from scratch.
Do you know why the E2D looks almost the same after all these decades? Because the platform works!
It's no different than why so many aircrafts look almost identical to those that flew 40,50,60 years ago like the C130 for example.