I mean, Occam's Razor says the simplest answer is that if no companies have shown competitive advantage from DEI despite massive investment in DEI initiatives that DEI doesn't work.

If you've ever interacted with a recruiting pipeline at a big company you know the recruiters spend way more effort trying to recruit the few "diverse" people than everyone else. There's not much talent you're missing out on. If 80% of CS grads at universities are male then your pipeline is 80% male. There's no 30% extra women that are somehow recruitable but missed by every firm out there. Those women don't exist, else they would have been hired already.

That's a good point. A think where it fail is that some candidates are not applying to classical channels (such as latin american) so recruters are not seing them.