One possible reason why women in the legion are treated so atrouciously is probably because of exactly that.
Caeser understands the power atrocities and fear can cause to his enemies.
Besides, in such a society as the Legion where the indivual is just another resource - and as such even high ranking oficials can be discarded if they don't appease Caeser's fucked notion of the greater good - women being slaves seem to be one of the few rewards good enough to keep your men fanatically devoted to you.
>durr Ceasar is who holds it all together
>the Legate is a mindless brute who can't lead shit
>it'll all turn to shit
>meet Lanius
>an even more striking presence than Edward
>commands double the authority
yeah, nah, the Legion will be alright
Their tactics aren't adapted to the wasteland.
They lost the 1st Battle of Hoover Dam because Caeser indoctrinated them that guns are for cowards, because of that the NCR Rangers just picked them off with rifles and explosives. And what their strategy for the 2nd Battle? The same shit, only this time they got more meat bags and a canon fodder - and even then the battle is a hard one for the Legion.
Ceaser says that pre-war structures and ideals don't have any place in a post-apocalyptic world, but we can also reverse that and say that antiquated notions of honor and valor hold no ground in a post-apocalyptic world - specially when your enemies have machine guns, plasma canons and power armor.
Altough the Legion's concept of honor is a contradictory one, since Caeser has no shame in making use of Vulpes - a master of deceit, infiltration and treachery - and employing unjust measures against others and their own.
The culture Caeser created reveres as him a god and when he dies, so will the Legion.
Their whole comand structure is entirely dependant on one man - when that foundation is gone, the legion will crumble.
And Caeser wisdom isn't that good to begin with. He likes to pretend that he lost the battle for the Dam against the NCR because of Joshua, and has that whole retarded logic of killing Legionnaires that use tech because "muh mankind needs warriors not tech to survive this moment derp".
Also have you ever noticed there's no old men in the Legion? That's because they despise weakness and any official that's too old gets killed by his sucessor. A big mistake, as men of wisdom besides Caeser is what the Legion sorely needs.
And without men of experience and wisdom the Legion can only be led that men like Lanius. Which even in war means they're fucked, as Lanius and his ilk only know brutality and have no foresight - pretty much confirmed since in the ending slides if Caeser lives, he choses not to pursue the Enclave remnants because he knew of the power at their disposal; while if Lanius becomes leader, he chases the remnants where he suffers a heavy loss and gains nothing.
They extended themselves over too much territory too quickly, in a way that they can't sustain as it burns their resources at a fast pace.
In fact they are more like raiders than a empire, since they don't produce anything of their own (except the babies the women pop out) and depend on the wealth of those they conquer to sustain themselves.
It would take all they have to conquer Nevada, which means losing the grip on the East. And if they did take Nevada, they would move to California where there was nothing to conquer and the only thing left for them to consume would be themselves.