Hi guys, first post here, long time lurker.
From what I gathered, the combination of surges manifests in a third "power". In the case of the windrunner lashings:
Gravitational surge - lashing to a distant point and flying(falling).
Adhesion surge - lashing and sticking two objects together.
Both surges together - full lashing, giving an object the ability to have its own gravitational field pulling everything to it and sticking there.
His fighting skill when protecting is a boon - but not one that has been confirmed to be THE uniquely windrunner ability.
I think for shallan, her ability to take memories is unique to her, not Lightweavers. The unique Lightweaver ability might be how she can transform people through their illusions - like she did with Gaz and the others.
Soulcasting at a distance then seems to me to be the unique elsecaller ability.
I might be totally wrong and a WoB has completely invalidated this hypothesis, in which case I'd like to ask for the relevant Wob to enlighten my ignorant self.