The 14 and 28 numbers are deceiving, 18650 start to sag at lower voltages, were a lipo does not, or not as much. You will Not get twice the battery life from 3 18650's as apposed to a 3s 1300mAH lipo.
I don't have a 3 18650 mod But running the same coils my 1300mAH lipo mods have better battery life than a dual 18650 mod.
The watt hour numbers are the only thing not deceiving you.
Also I don't buy lipo mods for the reasons i listed.