Your entire point is predicated on the assumption we don't, and so your whole argument falls.
For example, what's unfalsifiable about "evidence shows racism and sexism is still rampant in executive appointments". It's verifiable and falsifiable. You can, in less than a minute with a search engine, find the percentages of women on executive boards.
You can verify the representations are not proportionate. There is no evidence that, if no oppression existed, the representations would be proportionate. This is a very basic and clear difference.
The NBA has a very high representation of black men, and a very low representation of Jewish or Hispanic men. This in no way proves racism is rampant in the NBA. The cause is likely other factors, and if you decided to "positively discriminate" against black men to "fix" this problem, you wouldn't actually be "fixing" anything. You'd just be rationalizing discriminating on a racial basis.