A year or two ago there was a lot of excitement about how low-level, close-to-metal access and various other buzzwords would result in big performance gains for games that adopted the new DirectX 12 API of Windows. The reality of course is that DirectX 12 is not a magic bullet and that a lot of work is required to benefit from its performance rewards.
Jurjen Katsman, the CEO of Nixxes, spoke at GDC 2017 about his experiences in porting DX11 games to DX12. Nixxes is the company behind the DirectX 12 render paths of Deus Ex: Mankind Divided and Rise of the Tomb Raider.
TechPowerUp covers the session in detail over here and overall gist seems to be that developers need to be realistic about DX12.
The presentation begins with the speaker talking about the disillusionment consumers have about DirectX 12, and how they're yet to see the kind of console-rivaling performance gains DirectX 12 was purported to bring. Besides lack of huge performance gains, consumers eagerly await the multi-GPU utopia that was promised to them, in which not only can you mix and match GPUs of your choice across models and brands, but also have them stack up their video memory - a feature exposed by DirectX 12, but which developers argue is easier said than done, in the real world. One of the key areas where DirectX 12 is designed to improve performance is by distributing rendering overhead evenly among many CPU cores, in a multi-core CPU. For high-performance desktop users with reasonably fast CPUs, the gains are negligible. This also goes for people gaming on higher resolutions, such as 1440p and 4K Ultra HD, where the frame-rates are low, and the performance is hence GPU-limited.