No matter how we put it, energy output of fission is nowhere near that of fusion. And ships in FL require excessive amounts of energy for magnetic confinement of plasma, resonance heating and not to mention all sorts of exotic weaponry. Indeed any possible losses of energy would be minimal due to the widespread use of superconductors, however the consumption would still be substantial.
Hence a fusion reactor (be it a tokamak, stellarator or something completely different 1k years in the future) to power all those systems seems practical. Not to mention the relative ease of obtaining fuel resources from planets. In twenty years (to be a bit more pessimistic than the officials) ITER will have an excess of power. The humanity's development must have stalled considerably in FL universe to account for the unreliability of such systems.
Although, when we think about it, the fact that something as squishy as a human, and not one hundred g withstanding AI, is still conducting combat operations in FL does indeed make a point.
