I?ll throw in my personal opinion on the subject. For starters, as far as the tweets are concerned, why not both?
Everyone seems to think that Kojima was "defending" his action in making Quiet erotic by saying we?ll feel sorry for her, or backpedalling from saying he made her more "erotic" for cosplaying purposes, why is that? Is it possible he wanted to do it for both reasons? Calling his reasoning an ?excuse? makes it sound like he was defending his decision, frankly I think it?s more likely he simply misjudged people?s reaction to the story-related reason behind it, and I think it?s a rather cynical and pessimistic view from the people who say "at least ADMIT to it", seriously if you?re going to take a tweet seriously, take them all, he damn well did.
That he wanted to give it a reason as well like he does with most aspects of the game doesn?t mean that wasn?t his desire. Not to mention a character can be fanservice AND have an interesting character without being devalued, look at Eva (admittedly Eva had a far more organic merging of the two aspects, but you better believe people got fanservice out of her).
Many aspects of Metal Gear have had thinly veiled reasons one either fools themselves into believing or simply accepts to get to the awesome aesthetics. Take Sahelanthropus, it is given a reason by Huey why it is a bipedal war mech despite the mountain of flaws such a design would add waaaay outnumbering any possible strengths. Suspension of disbelief, and it looks damn cool in my opinion. I understand in some cases no answer may actually be stronger than a handwave one (is there any explanation for the exploding rock thing it does?), but they both have a place in stories.
Honestly I?m not a fan of Quiet?s outfit, apart from maybe the torn leggings being a nice touch as I can imagine them getting damaged from speed-running through underbrush. I certainly wouldn?t call it ?boring? though, gives a distinct silhouette. I mean, people are saying the XOF uniform looks good? Its dull grey military garb, *yaaaawn*. Give me something like Mantis' bondage suit and gasmask or Ocelot's cowboy outfit with a shotgun bandolier anyday (no offense meant, that?s my personal opinion and I understand some people might really like the look, I?m just being a tosser giving a counter-opinion here). That being said, I've heard some design choices from people against the outfit I honestly do think would look cooler (and probably sexier, but ho hum).
Honestly, I think it?s mostly just rotten timing, fanservice and female characters in general are a hot-button topic right now, and it?s a lot easier to suspend your disbelief for things you actually like or don?t think about too much. I suspect an engineer might struggle believing Sahelanthropus' design more than someone else. Is it a bad outfit? Well, I?m sure there?s an audience who enjoy it at the very least, and I wish I was a part of it. But aahh well.