I have noticed a couple of folks that had servo failures in the bigger engines so far. it seemed to happen where the modeller had used a straight stiff piano wire pushrod too.
I think it is more of a problem with the stronger engine vibrations that cause the throttle servo to fail.
The engine vibrations impart a strong forward and back movement that stresses the servo gears more.
If you use a straight piano wire pushrod, then it tends to force the servo to hold its position more and thus stresses the gears and the servo output drive transistors too.
So I think it is better to use a flex cable or even nyrod for the pushrod to control the throttle. That way you have a little give or slight sponginess there to reduce the stress on the servo.
When you think about it, the bigger engine vibrates a lot more strongly than the smaller engines do. Then the fuselage itself also vibrates. Between the two you get a strong high speed movement or flex between them to occur and that can cause a stiff pushrod to push and pull on the servo arm, which forces the servo electronics to be constantly trying to fight it. So the servo gears might fail or the output driver transistors overheat and fail.