Basically, in Light Armor most of your protection comes from your agility and avoiding attacks. Basic leather and cloth aren't going to give that much more protection.
AC: 10 is the level of ability the person with average (9-10) Dex has to dodge/avoid blows.
Light armor adds a little bit but not much mitigation to this, which makes sense, really. Leather realistically is only going to give significant protection from environmental hazards like basic thorny vines. Leather is not going to do much to stop a sword, arrow, mace, or axe.
Thicker, armor-grade leathers like cuir bouilli, or cloth-type armors like gambesons, should probably be at least studded leather stats, and may be on the low end of Medium armor. Brigandine is leaning toward the stats of breastplate and halfplate...maybe even Ringmail.
Japanese style bamboo armors are also medium to heavy armors.
Light armor stuff...realistically is people wearing sturdy work gear because they can't get something better.
