We've done some serious battle testing with rudder only (no airleron) high dihedral combat planes with shoulder mounted wings. There have also been several experiments (VERY Successful!) with high dihedral low winged scale combat planes controlled with rudder only (no ailerons). We have found that the more dihedral, the more they become self righting, but there is a trade off. I can't explain it in big educated terms, but...

Take a 48" wing.

3" dihedral...little self righting but very stable. Rudder control rather slow.

5" dihedral...self righting getting better...stability ok, but getting much quicker on rudder control

7" dihedral...really good self righting, VERY quick roll axis control with the rudder, this is a sweet spot for rudder only combat planes. You also begin to get a noticable in flight tail wobble as the vertical and wing work to keep the plane upright (as if they start fighting eachother for control of the plane)

10" dihedral...when you let go of the sticks it can't right itself fast enough! Even from inverted it flips over like a weeble. Self righting is amazing...but the trade off is stability. The rudder becomes EXTREAMLY sensitive (snap roll city!) and the inflight tail wobble becomes severe. This is also about the point that you start loosing lift and pitch control starts becoming less effective.