You are also right about synthetic hydrocarbons. The extra hydrocarbon synthesis step lowers the total efficiency, compared with using hydrogen.

Nevertheless, the lower efficiency is more than compensated by the simpler methods used for storage and handling, which require much less expensive materials and a much lower volume and total mass.

The benefits of using hydrocarbons for long-term energy storage have been amply demonstrated by the living beings that have been using this method for billions of years, many of which can easily achieve an autonomy of months without eating, while doing activities that would make a present-time robot using batteries inoperational after a few hours at most.