Sure, it is reasoably easy to say that A is more efficient than B, and even quantify how much energy A saves in comparison to B. But that is only a relative mea

Sure, it is reasoably easy to say that A is more efficient than B, and even quantify how much energy A saves in comparison to B. But that is only a relative measure; it is far less obvious how you'd quantify the waste in absolute terms like the chart in question here seems to do? To do so you'd need to know some theoretical ideal minimum energy process that would get some equivalent end result as a reference point, but that seems wildly infeasible to estimate