The carts were pretty fast, so they could cross the first floors without being blocked by the tyrants. With that in mind, Billy and the others used them. However, they used long-ranged attacks to kill them anyway. It would be a waste of experience not to do that.
Usually, one would need around four hours to cross the first floor while walking nonstop, but with the carts, they did it in ten minutes. Billy could make them go even faster, but that might risk them dropping the materials collected along the hunts.
"Have you ever thought of making trains, Billy?" Icarus asked.
"Yes, but I couldn't be bothered," Billy replied. "I don't mind helping this world develop, but I am not planning to become everyone's slave to bring prosperity to this world."
"Well… It would take a while for the rails to be built, so I understand where you are coming from," Icarus said.