I look at Vb another way. It is the speed that gives you the max positive or negative Gs and still fly generally straight and level.
This is with respect to not trying to full deflect any one control surface. Va is the speed at which a control surface with stall with full deflection prior to structural damage. There is a difference there.
Side note my airplane manufacture says at any speed if you go full deflection in one directed immediately followed by full deflection in the other direction it will do structural damage! Yikes!