There are many Mars mission profiles that use insitu propellant production. Mars' atmosphere has a high enough methane content to produce a return fuel load.
Most mission profiles using this method would have an automated production facility landed in advance of the manned mission. Thus assuring the fuel is ready and waiting before the manned mission arrives.
Mars gravity IS
low enough for single stage to orbit. I have never seen a mars mission profile requiring 2 stages to achieve orbit from the surface of mars.