It is equally difficult to build an equivalent of the modern-day bikini top, since they almost always rely on the elasticity of the material to stay in place and cover what needs to be covered. However, in theory a long scarf and a few ribbons can be as effective as a modern day sports bra, if your goal is to keep involuntary movement to a minimum, as long as you wrap and tie tightly enough. Not all women are built like Pamela Anderson, after all. Especially not those who spend their adolescence pushing their bodies towards peak physical performance - look at the average female gymnasts and ballerinas, for example.
Remember, our goal here is function, not form. If a female warrior's top priority when she dresses for work is to look sexy, what she chooses to wear isn't really the problem. So a non-elastic bikini on the amazon who fights alongside the bare-chested barbarian makes perfect sense to me.
I feel like I'm getting way too close to the realm of what the forum rules call "inappropriate topics" as we keep talking about this.. I should probably shut up now.
Please stop confusing things by using common sense like that.