The book itself has a section at the end outlining the weaknesses. The section is more than lip-service, and I was impressed by the honesty.

But I thought they missed the main one.

The biggest weakness is that you typically need a revenue firehose to sustain such fluidity. Stronger organization forms nearly always emerge in response to a sudden cost-control imperative, because fluid models buy creativity at the expense of cost efficiency.

There comes a time in every company's life when the first cash cows start to die. That's when such models are really tested.

Scaling used to be a problem, but increasingly it is not. Now it's down to money.

Kinda related, this reminds me of a Soviet era joke.

"Comarade, if you had two houses, would you give me one?"

"Of course!"

"If you had two cars, would you give me one?"

"Without a doubt!"

"If you had two shirts, would you give me one?"

"NO!"

"Why not?"

"Err... I actually HAVE two shirts."

Moral of the story: when money finally decides to talk, people listen. I'll wait to react properly to the Valve model when they have a couple of bad quarters in a row.