The argument IE6 was that the web grew too stagnant with a single dominant web renderer. If we all agree that the Web is a better place with multiple competing web renderers, why wish the death of the Edge renderer when it and Firefox are all that are standing in the way (and barely by latest metrics) of forks from the KHTML/WebKit/Blink family dominating?
Did you mean to say Direct3D? That's still leave you with input, sound, maths, and 2D missing.
That view is fairly one-sided, to say the least. The history is presented in this StackExchange thread: https://softwareengineering.stackexchange.com/questions/6054....
But to summarize: OpenGL was the standard before D3D was created. D3D has been a step behind OpenGL in features and performance up to about D3Dv7. Then the OpenGL ARB screwed up, with Microsoft among the members (some hypothesize that Microsoft were attempting to sabotage OpenGL).
* Direct3D being open-sourced would have removed the need for Vulkan.
* Many compilers are good for the ecosystem.
* Many browsers are good for the ecosystem.
It's only a choice if we have open standards so you can actually choose between different implementations.
* Drop MSVC for Clang or GCC
* Drop Edge for Firefox or Chromium
because they love open-source, right?