But I don't see how we are doomed in the long run. Not in the next 200 years, at any rate.
This may be a big part of the difficulty, right here. 200 more years isn't "in the long run" for me. As a child, I lived in a town that celebrated its 1200th birthday. Growth can't continue forever, because resources, including energy, are finite. It may well be able to continue for 200 years, with innovation, though I think that is unlikely. But not in the long run. In the really long run, things look bad for the earth when the sun swells into a red giant.
In a world where the population will eventually stop growing, and then will decline, do we really need ever more energy, above and beyond what can be gained through efficiency, in order to have improving lives and a growing economy?
This is another confusing point. If the population is declining, how do we keep the economy growing? I can see how the standard of living could continue to improve, but not how the total economy can grow. Talking about the per-capita economy is different from talking about the total economy. Which are you writing about?