Your part of the pull coming from the industry is right. That's about he only thing that's true.

AMD never bothered to involve Intel or Nvidia during the development of Mantle.

That's not a way to come up with a a new API. That's a way to ensure that you get to design it completely around your own strengths and ensure a competitive advantage.

Furthermore, even after it was released as a beta, Intel asked about participating in Mantle and was rebuffed.

http://techreport.com/news/26682/intel-asked-amd-for-mantle-api-spec

That is exactly in line with AMD trying to reserve pole position for as long as possible.

It's only when they didn't get the traction on Mantle that they wanted that Vulkan came into existence. Which, as it should be for a broad API, took two years to nail down. It has Mantle as a basis, but it also has a bunch of things of other features. And by the time it was released, it was already largely made irrelevant by DX12.

In the link that you provide, Nvidia says that they're committed to DX12, not Mantle. So I don't know what you were smoking when you wrote that DX12 backfired on them.