Well for starters, the inner limb doesn't bend a whole lot more on a molle than on a full working limb bow. Think of putting a long stick on the tip of your finger: you only have to bend your finger a tiny bit to move the tip of the stick ten inches. Now make that stick very stiff but light and compare using it to propel something stuck on its end to propelling something stuck on the end of your finger.
The advantages are still up for debate, but all my fastest bows per draw weight have been mollegabets. The idea behind mass efficiency is that if you make a narrow, thick lever it can be lighter than a wide, thin working limb, and therefore reach higher speeds in the same distance. String angles are also less severe, and those light levers translate to low/no hand shock.