And there is also the design consideration that bkdavy mentions.

Here are a couple of pictures made up for this same topic awhile back. They basically illustrate his point.

The red area is how much the same movement creates in the carb. Couple of degrees up from low motor in the picture showing a tiny bit of red. And the same amount from WOT.

The movement of a servo however is from a rotation to linear, and at either end of the servo movement, the fore/aft is less for the angular change. You can do a lot to reduce this "softening" by making servo arm connection long so that the servo doesn't go full rotation to get full carb movement.