I couldn't imagine storming the base on Mars with only the basic starter rifles in the MicroProse version. Though apart from the Hovertanks it might be actually doable.

That said I watched a friend play the fireaxis version of XCOM2 and he never put his troops into cover, just had them standing out in the open - yet somehow managed to beat the game using this "strategy". He blew through troops like tissues during flu season though.