efficient is the key. It's about outcomes. There's nothing saying we need greater quantities of energy, because very little of the things we as a civilization do are fundamentally energy-limited.

Over the long term, there is no shortage of energy. Unless you're going to argue about Dyson-sphere limits, the Sun provides an amount of energy far in excess of what we'd need. On that scale, the total energy available through fossil fuels and nuclear fission is a drop in the proverbial ocean.