Alas, I think you are correct.
One of the people I talked with when writing the book was a young woman who worked for a financial services firm. She loved her job, loved the culture, but told me that she was going to have to leave because the only way to get a promotion was to go to another firm, then return later.
In practice, it's highly inefficient to expect one company to handle all your promotions. Even if you're ready to take on a higher level of responsibility, there's absolutely no guarantee that they have a position open at that level.
That's why the alliance model makes sense: you might be going elsewhere to find an open promotion, but that shouldn't imply "disloyalty."
This might be a function of broken promotion processes. Perhaps, in a world in which employees believed that they could advance their careers by either staying at one company or moving around, we would see a significant fraction of workers who would want to have long tenures.