&gt; not something that aligns to a specific browser vendor’s agenda or just come out &amp; say that your test is for how well other browsers match your favourite 

The metrics reported on caniuse.com is based off of a publicly available test suite.  Are you saying that caniuse's tests are biased and not representative?  If so, can you provide some examples?

&gt; Microsoft has to pay for the sins of the past. But if you don’t reward someone for improving their behaviour, what incentive is there to ever improve?

As a publicly-traded company, Microsoft's incentive to improve is ultimately driven by their shareholders, and not by some murky idea of reciprocity.

Therefore, web developers, having seen Microsoft cede majority market share to its collective competitors, can simply elect to support the majority knowing that Microsoft must improve just to stay in the game.