It's really really not, you can see it in the data. I took GDP per capita and kg oil equivalent energy consumption per capita and in 1970 the very year the article highlights as us falling off the HA curve and representing 'lost' GDP the exact opposite happens. We begin producing way more GDP per capita using the same unit of energy.

It's basically a piece wise function if you graph it. 1960 to 1970 the GPD/energy unit ratio is largely stable then after that it begins increasing monotonically going from .69 to 7.94.

https://news.ycombinator.com/item?id=41392222

It's represented everywhere that efficiency counts. I haven't fact-checked it, but one source[0] claims that refinements in the design of soda cans (thinner walls, different shapes) since 1960 saves "at least 90 million kilograms of aluminum annually."

[0] https://www.youtube.com/watch?v=hUhisi2FBuw

It's also irrelevant as anything other than a limiting case. The issue is with the statement that energy use must go up to produce more GDP or that not increasing energy use means we cannot raise GDP or even that GDP is limited by a flat energy use.

USA GDP is still on basically the same exponential curve, yet energy is flat. That's the counter example. The rest is exposition.