DX12 seems to be more helpful for PC games, less so for consoles.
"If your game is bottlenecked by the CPU, going to DirectX 12 or Vulkan will greatly help your game. But if you are bottlenecked by the GPU then the updated APIs will help little or not at all. Since many PC games are bottlenecked by the CPU, you will see massive gains there. However console games are usually bottlenecked by the GPU so I would not expect significant changes from newer APIs. The GPU is the same regardless of if you are using OpenGL, DirectX11/12, or Vulkan."
"So if your game is bottlenecked by the overhead of telling the GPU what you want to do, then the APIs are a huge help. This situation happens a lot on PC games where you have a powerful card sitting idle because it can draw things faster than it can be told to draw them. But console games tend to keep the GPU working hard so there are less gains to be made."
- developer John Hable on DirectX 12. His Twitter bio currently says he's a rendering programmer at Epic working on UE.
gamingbolt.com