I guess I'm technically a "person of color" (Hispanic) but I have a ton of useful, valuable experience and so far as code monkeys go I'm pretty good at negotiation. I thought Microsoft was a horrible pit of vipers and a generally terrible company, but I definitely did NOT experience any racism.
Maybe the people who responded to the survey are generally just really bad at negotiation, and the HR people should've gone easier on them.. I don't think it's feasible to get a 50% pay bump without changing jobs, so they're all in a really awful position
I got unlucky and ended up on a particularly bad team, so I left before I could get any firsthand experience with it. It's weird if it works that way, though, since it's so easy to jump ship to another company and get way more money.. Microsoft's interview process is as hard as pretty much any other high end company (except maybe Google, which seems to expect you to grind on leetcode a lot more..)
I think you're right about there being selection bias... people who are happy with their package don't spend their time filling out these spreadsheets (I didn't!)
Also, I note that if I had taken just my initial offer, my TC would have been much closer to the listed. But I went through the long and arduous process of sending one email to my recruiter asking for more money and here I am.