DirectX 9 is a solid API, I don't think anyone is questioning that. With a few updates it's lasted almost 10 years, and remains prevalent despite Microsoft releasing two successors. Great-looking games can still be made with DirectX9.
The point is, I think, that as much as DirectX 9 can do, DirectX 11 can do more. Tessellation can add detail to artwork. More realistic lighting systems can be implemented without taxing the system as much as it would in DirectX 9. It makes programming games for multi-threading easier. DirectX 11's potential is greater.
Why don't we see games truly meeting that potential, though? Because they're still coding for DirectX 9 as well. Almost no game developer wants to lock out XP users and users still using pre-DirectX 10 hardware, thus games at their core must be compatible with DX9. Only once DX9 is left behind can DirectX 11 reach its full potential. Two things probably need to happen for developers to get on board with that: first, XP's market share must shrink so that it doesn't matter anymore. Secondly, Microsoft needs to release a new console based on DirectX 11. Battlefield 3 is the single game coming up that will only support DX10 and DX11 on PC, but it's still being made to be compatible with the DirectX 9-based Xbox 360.
A PC-only game is not tied down by needs of consolization, and can be made for DirectX 10/11 only. They have the opportunity not only to add DirectX 11 but to make it from the ground up for DirectX 11. If they did, it could be better than The Witcher 2. PC gamers feel let down if a PC exclusive game does not meet its full potential.
Again we are making excuses for why Dx11 has failed to impress. That DX11 potential you are talking about have been talked to death since 2009. And it still remains a speculation without any solid proof. Besides without a DX9 render path to compare to, how do we know what has been improved in a DX11 game. DX9 sure made a dramatic difference in lighting/ shading over DX8 and games with BOTH DX8 and DX9 render path prove it. (example COD3)