In reply to La benya:
> leg loops are just there to stop you flipping around. if you're falling with such force that you risk internal organ damage, you're doing something wrong
Back in the day there was a thing called a Swami Belt. Just a wide webbing belt that was held on by either the climbing rope knot or a short length of knotted tape.
It felt comfy until you weighted it. Even a tight rope seconding would see it start to rise and constrict your stomach, your breathing and it would dig into your lower ribs.
I never took a lead fall on one and certainly wouldn't have wanted to.
The first proper two piece harness, ignoring the one piece Whillans, was probably the Troll Mark Five and was a complete game changer for leading and probably helped push grades as much as any other piece of climbing equipment as leaders could finally fall off in a previously unobtainable level of safety and comfort.
Todays harnesses are basically exactly the same design with softer, lighter and more comfortable fabrics.
Leg loops are a vital part of any sit harness. As a previous poster has suggested go and try lowering off a route on just a belt.