Linux and Windows do not have a goal of perfectly emulating the other one, to the degree of sharing the same spec and tests. Not sure how this example applies, especially since Blink is open source, while Windows is not.

In fact your example betrays you, because it would be like rewriting Linux from scratch while still attempting to maintain perfect compatibly with Linux. And then arguing that you've somehow weakened Linux in the process. Why not just fork it and maintain your own fork?