I considered one rudder = one servo at app. 1/4 more area than both elevator halves combined with one servo each. On its side, in knife edge, the rudder is now acting as elevator, one servo is working more area, as opposed to two doing the same control on elevator. Also, on its side, there is no benefit of wing lift, so is it working harder than elevator, on its side?
I hear you on the ailerons, although larger in area, its spread out the width of the wing and as you stated, doesn't change the attitude of the model or carry as much extended force. Interesting. Joe