A good number of his memories *are* missing, or at least unavailable to him currently, for those 300 years he was making mostly identical and unimportant memories that would mesh together rather than overwriting his important ones. They do have synthetic organs to a degree, that's what they're implanting into carriers after they take their organs. They're using carriers as living bioreactors, not entirely sure why they haven't made a replacement for them but I assume that like with Cyrus's heart, the people who would be making such improvements would either not work there or dispose of themselves to avoid the control of or giving power to Darius. They have things they *could* use as fuel but they're relying on kinetic energy to charge batteries, could be that they prefer clean energy? And if you have ports like that, airplanes aren't necessary or efficient. Other countries outside of the port network probably wouldn't allow traffic from their country anyways given the bad relations mentioned.