unfortunately dx12 blows across the board still. For example on Hitman, which allows you to toggle between DX11 and DX12, I keep trying DX12 but it has all kinds of issues with full screen mode. No way to do exclusive full screen (fine) but the fsm it implements makes the game window disappear when you alt-tab, whereas the DX11 version just stays behind as a background window so you can still see whats going on, and even runs while you are tabbed away (DX12 auto pauses). It stutters when I alt tab away and back in, no stutter at all with DX11. Same problem with Forza 6 Apex and Quantum Break, except as the latter as UWP games you are forced to do DX12, no choice.
As an ID software guy said, there is literally no reason to ever use DX12 over Vulkan/DX11 since WIn7 is incompatible with DX12 and still is 50% of the gaming market, you have to make a DX11 version no matter what. The DX12 implementations for xbone and PC are very different and require different code paths so you save no cross-platform time with it.
Their SLI stance too makes it difficult, DX12 removes driver SLI optimizations so games have to SLI optimize themselves, and engines never do that. While theoretically the idea that DX12 can just use multiple cards natively without requiring SLI is great, in reality it means games have to specially code for multiple GPUs. No one is going to do that.