Actually, you can account for the "scale speed" issue though the use of Renylds number (I can't spell it to save my life and I'm too lazy to look it up).

Re is a function of wing chord and airspeed, so a smaller wing flying at a higher speed has a simular Re of a larger wing moving slower (if I remember that right, I might have it backwards)

Weight and wingloading effects, however, are much messier. You can approximate wingloading effects using a volume loading instead of a area loading. You can calculate the volume loading the hard way, using the true volume of the wing, or with a shorthand way that only works as long as you compare simular airfoils at simular Re values, but even the short hand ways are pretty good for most messing around.

But the general statement that scale models usually have lighter wingloadings and higher power loadings than larger counterparts is acurate. Though when you keep it in the model realm, larger models usually have lighter loadings than small ones. So it's not a linear "smaller is lighter loaded" thing at all.