This is only true when estimates are in concrete units, the way we did it in the 80s and 90s. Unfortunately that still impacts contract structure today and it's

This is only true when estimates are in concrete units, the way we did it in the 80s and 90s. Unfortunately that still impacts contract structure today and it's hard to change on that level. TFA is talking about estimates inside projects, which are not time based anymore in any environment that cares about the problems you laid out. Personally I offer my customers to either pay by the week, or pay by extremely fixed scope with a 3 month definition period up front and a 50% buffer above the estimate. I stress that paying by the sprint lets them change objectives at any time, gives them an always-current report of how much "effort budget" they have left to work with, and guarantees they only pay for what they use. That felt like a risky move the first time I did it, but I never lost any business over it.