To me, efficiency means achieving a desired goal while consuming a minimum of resources (time, energy, space, …).

If the goal is defined in a too narrow scope, i.e. your ‚dumb‘ definition of efficiency, the flexibility may be missing. Still, that particular goal may be reached efficiently.

So it’s not an issue with the definition of efficiency, but rather with scoping the problem. As the article states, it may not always be possible to scope the problem in an easily measurable way, hence optimizing for proxy targets.