Yeah ist gives the minimum (ideal) energy for the assumed state (p = absolute zero pressure), but the state itself is unrealistic and poses the maximal necessary energy required to achieve that state (compared to realistic ones with some mbar).
More Work has to be done if you pump out 100% rather than <100%.
The statement on the pumping efficiency is correct.
Well the energy to pump down to 1 mbar (for the tube that size) is around 0.5 TJ when using a linear formula
The energy required to pump to 0 mbar (again when using that formula) is considered 0.5 TJ, however realistically it would require an infinite amount of energy.
I do understand where you are coming from but for the vast majority of the population, I would like to keep it somewhat simplistic. I am not trying to argue with you, just stating why I stated it was a lower limit (as an approximation)