In terms of measuring performance of the aircraft, you do indeed just throw it overboard. Obviously the energy system as a whole need to take into account the dumping of hydrocarbons into the atmosphere but I believe the parent commenter does that by suggesting synthetic fuels created through carbon capture.

Anyway, my point is just that when comparing two aircraft, and their fuel sources, it’s probably worth just comparing the closed system of the aircraft and measuring the environmental impact of fuel sources separately.