You take a lot of really smart people and get them to work together, and most of them are going to feel like they're not as smart as their peers.
Anything that creates self-doubt is going to really fuck up their retention.
Anyone who writes a manifesto to do just that should expect they'll be promptly walked out of the building.
Can you elaborate on that one? I'm really curious, as my naive assumption would be that impostor syndrome should improve retention (something like "I'm not as good as my current employer and coworkers think I am, so I better not change jobs because this is the best I could get").
That makes it pretty easy to take a new gig and make that nagging imposter voice in your head quiet down.
"I work at the world's most powerful tech company, get paid embarrassing sums of money to do it, and get good reviews from my manager. But I don't feel super smart, so I quit."
When you come in as a newbie, and you see all these people seemingly directing themselves effortlessly, and creating cool shit day in and day out, it can be seriously soul crushing. You're still on your tricycle trying to figure out how to do anything at Google, and aside from your laptop, virtually everything is a technology that is Google specific and shares almost nothing with anything you've touched before.
Between those two things, a lot of people feel like they'll never make it. They hold on for their 1 year anniversary if they can and then shop their new Google experience around to find a good exit.
It only hurts because it is plausible and causes self-doubt.
But Google can prove this conclusively just by plotting the distribution of performance reviews between "diversity hires" and the regular pool of employees. You either show that there are negligible differences (the diversity program works) or the guy is right (the average bar did get lowered).
Google will never publish this data because they are cowards.