I don't see any reasons to add a serious supply system for Humankind as warfare is just part of the game, not the whole focus. Adding supply wagons as a unit would not add anything to the game, supply train is basically already represented by the flag in combat anyway. The game is already quite generous for the defender, ability to build fortifications that increase combat strength and getting militia units to defend cities. If there is obstacles needed, it should be things like making it harder to expand everywhere and control the whole map, administrators hardly did anything in Lucy. The only serious thing lacked on the military side was how you could field an arbitary amount of armies and units, adding maintaince cost like in endless legends would be a help here. Overall the combat part of the game seemed to work quite well in Lucy, the economy part and city part however seems like it needs some work.