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If a woman is wearing bikini armor then most of the time when they avoid damage it's by some form of parrying or dodging, so it really isn't an issue of logic then.

Sure you could argue that bikini armor defeats the purpose of armor to begin with but then you have to remember that in reality, most warriors were never fully protected. Their vitals were, which is really the main flaw of bikini armor, but this is fantasy world. Why not show a little cleavage when you're fast enough to dodge arrows?

It's nice to look at.

Really, where the line should be drawn depends on who is telling the story. If someone can sell a story with a chick wearing bikini armor, then why not? As the article suggests, it may be appropriate for the culture. That's what really should matter. So yeah, I think taking into consideration how something exists in your fantasy universe means a lot more than how practical its design might be. You can play around with it to the extent that the inherent deficiencies based on design alone don't matter. You can't justify the things that really don't fit though, usually.

Hauberks, or chain shirts, are heavy and not really needed. Leather armor would do just fine and provide adequate protection.

But basing it on the size of their weapon? I don't see how that works. What about the type of dagger they might be using? Some are significantly larger than others. Why would they need a hauberk if they're wielding a rapier or a longsword? Sure, the weapons are dangerous, but it's not like wearing heavier armor is going to help you wield them better.

A mage can wear more than robes, and besides, shouldn't the same thing apply to them? Some aren't half bad at swinging those who staffs around. And even though cloth armor itself isn't going to offer the same protection as hardened leather, riveted plates, and so on, it can't just be said it protects from nothing. If it's made as more specifically it can help cushion some blunt damage, and at the very least it offers a layer of protection against outside elements. It would be just as important for a mage to have their whole body covered even in robes to protect themselves from ACID RAIN!!!! as it would any other class with any other kind of armor.