It seems I was for the most part right. DirectX 12 has been largely a failure.

Here’s a link:
http://wccftech.com/project-cars-dev-dx12-improve-performance-3040/

Project CARS developers have been quite open about the development of the game. They have taken to the forums to solve all the issues that the players have and had to face. From bugs to future releases, they have been quite open and cooperative to the fans about their plans and have hence received appreciation as well for it as well.

When asked about the impact of DX12 on Project CARS, the Head of Studios at Slightly Mad Studios, Ian Bell revealed to the fans that the new API will increase the performance of Project CARS by 30-40% which is surprisingly quite a major performance boost. The new API will be making its way into users hands with the release of Windows 10 which is a free upgrade to any PC running a previous version of Windows.

Project Cars 2 is released today. It has no support for DX12 at all.