"It's simply unimaginable that this loss of talent hasn't had a huge impact on the company."
I think it would have done if the rank-and-yank/up-or-out happened when we were a 6,000-ish person company. They had just opened RedWest while I was there and were working on the new buildings across from the main campus. I think they were talking about the Issaquah campus right around the time I left as well.
It was clear that the company was growing and things were changing. There was even talk about not granting stock to new hires anymore, which has obviously been reversed. However, this was heresy at the time. (Mind you, most of us were thinking we were past the guaranteed "millionaire" stage and thinking that a stock grant would cash out for a down payment on a nice house.)
Now it's most definitely a "big" company, and you don't need that many people who would earn 1s in their reviews and get promoted every year. A company like that needs a lot of consistent contributors. If you let some good people fall through the cracks, even if it's 10%, the company can continue for years.