I think that what he/she is trying to say is that many feminists go around like "OMG stop oppressing me, I can wear whatever the hell I want! Let women walk outside bare chested! Blah blah!" but when they see a woman in a game/movie wearing a sexy outfit they go nuts. He has a good point and I've seen many woman do that in real life, but it does not really applies in this scenario/subject we are talking about.
It's a complicated subject. On one hand, yes, women can dress however they choose and should not be harassed or, even worse, raped for it. That's not the point being made here though, as you intuited. Here's the thing, it's one thing for a real woman to choose how she wants to dress and another thing to be told by society that she must present a certain way. It's problematic when women are only depicted in one way by, primarily, men. And let's face it, advertising, movies, tv, video games, comics,etc usually depict women as sexy. So were sending two messages, one is that women are only valued for their sexuality and at the same time are responsible for what happens to them (rape) when they dress sexy.
How does this relate to armor in Mass Effect? Well, we're being shown that a woman's purpose is to be sexy at all times even when she's in combat. It's stupid. It's insulting. It's degrading. And, I, as a consumer of this product am going to complain. Loudly.