I agree with rudder servo being stressed out a bit. That is only one control surface to control entire plane. On mine I removed the stock rudder and replaced with a longer one with more surface area. So far so good. We shall see what goes first, the servo or rudder.

As for the ailerons you really don't need a ton of torque out there. Once you give input it goes in that direction. Unless you are in a flat spin. Now for the rudder and elevator they need strong holding power and torque. Digitals work well there because of the better holding power but not a must have. Just something nice have the get the most out of your plane. Mainly the rudder then elevators next. Flying normal the elevators are not really under much stress. But doing waterfalls where you hit throttle wide open for a second to get tail over then again to repeat there is some torque needed. Snap rolls or tumbles on 3D rates can be stressful also. A good reason why there is a carbon fiber rod in tail. Without them the horizontals would break.