To your first point, I had a very productive project where instead of as in the article the devs become managers, our project manager was brought very much into

To your first point, I had a very productive project where instead of as in the article the devs become managers, our project manager was brought very much into the dev team, almost as a tester, using the product daily. He became attuned to the pace of development and never over-promised anything. To your second point, I've had projects where I simply assigned a day to every task, and it turned out remarkably accurate.