Why simple paper planes fly better than most "realistic" paper plane models?
The reason is really the size! Air molecules have the same size if they flow around a small paper airplane or a big real airplane, but since their relative size is so much smaller when they flow around the real airplane, friction effects are much smaller for the big airplane. When comparing airplanes of different sizes, a dimensionless number first formulated by Osborne Reynolds is most helpful. It is basically the ratio of inertial to viscous forces in the airflow, and the formula is
$$Re = \frac{l \cdot v}{\nu}$$
Nomenclature:
$Re\:\:\:$ Reynolds number
$l\:\:\:\:\:\:$ characteristic length, for example wing chord
$v\:\:\:\:\:$ airspeed
$\nu\:\:\:\:\:$ kinematic viscosity of air

Flows with the same Reynolds number behave identically, but your scaled-down aircraft flies at a very different Reynolds number than the original (both speed and characteristic length are a lot lower), so the airflow around it will be very different. For it, the air looks more like a syrup when that around the original is like flowing water! Therefore, lift creation needs different means at this scale (wings with more chord, for example), and the paper airplane is better suited to cope with this particular flow condition.

The next difference is wing loading: The paper airplane is very light; its mass per area is low. Therefore, it can fly at a slower speed than your scaled-down real airplane, and it will be easier for you to launch the paper airplane properly into the air. The scaled-down airplane needs to be thrown harder, but still straight, and this might be another reason for it falling down quickly.