What I wonder is, how much of this is simply inevitable? As a company grows larger it is bound to have more bureaucracy and become more sluggish. The best and brightest, especially those looking to work somewhere that is more agile will inevitably leave which causes a slow and painful brain drain in the company.

I have to think this has happened at most other tech companies in the past. I am sure at one time, Microsoft was looked at as a great place to work. Apple may have experienced a similar brain drain, especially in the 90s when Steve Jobs was out.

Then I have to wonder how you can counteract it. The only thing I can really think of is maybe if you ran the company like a decentralized flat organization where teams/products are virtually autonomous. I can only think of maybe one case where this has worked out, but its outside of tech.