The benefit of DX11 over DX9 is that is offloads to the GPU much of the processing from the CPU that bottlenecks performance. Probably because the CPU has to draw so any objects in a sim and run FMs etc. This allows weaker CPUs to run the game much better. That higher frame rate is obviously a benefit running VR but VR was not the reason EDGE was created.
The benefits of DX11 over DX9 are probably way too numerous to mention. DX9 is so, well yesterday. Now DX12 is around the corner.
Even Maddox realized that with Cliffs all those years ago, albeit with way too large an ambition.
Now I am not taking away from 1CGS, it is very apparent why they chose the route they did, they already had all the code from ROF which was DX9, could deliver a WWII sim in a short period of time, which I am sure was important to 1C to keep the franchise moving and why they elected for this joint venture with 777 to start with. To try and adapt code from Cliffs for BOS, I am sure would have been a nightmare, especially with so many parts of it being somewhat broken.
I don't think there is any doubt though, DX9 has pretty much seen it's day for the future. Obviously ED knew that quite some time ago, and are planning appropriately for the future. The limitations of DX9 are easily seen in the performance issues it has in today's sims.
Only time will tell what 1CGS will do for the future.