Along with legs, you also have arms and neck. A vest or short-sleeve shirt of maille, or a breastplate of some sort, provides very intermittent protection. A true hauberk covers the arms down to the gauntlets, and usually the neck (traditionally integrated into the coif). A blade dragged across one (or an arrow deflected from it or whatever) will likely contact meat somewhere before the attack is finished, while the other will just hit more metal.
Also, maille comes in a wide variety of weights and designs. Some poetic license was taken in estimating exactly how much maille we were talking about. I mean, if you're going to make a small vest of maille, you probably want light. If you're building something head-to-toe, you design for max protective value, since the chance for "light" went out the window long ago. Weights can realistically vary by 300% or more for a given surface area, based on weight of wire and size of rings - and the protective value corresponds roughly to the weight. This was not specifically stated, but it was not specifically denied either, so I had to guess.
And for the Native version, since I had no historical basis, I had to just throw things together based on how they were used previously. (Since I didn't change the troops file.) A much better set of examples exist in the Holy War beta, if it ever gets finished and released, and I'm working up something for ASLOW that will have a more feasible breakdown of armor weights, values, and deployment. (ASLOW has been a project, for sure. Fiction writing is MUCH more complex than history... and ex_otto is a decent writer, but he's not much of a fighter or an armorer.)
Of course, the only two mods with working RCM versions released right now are ONR and Mesoamerica, and both of them have highly specialized item lists. You almost have to be an expert on Japanese combat to even PLAY Onin-no-Ran. Neither of these help you much with game balance on what you are doing.