As Udo pointed out, this is how the designer meets the requirement for
increasing "up elevator" force as speed increases. While this has a
safety advantage, the truly determined performance oriented pilot will
sometimes remove the undercamber to reduce drag. I've never wanted to do
it, because I want the safety advantage and I'm concerned the weight of
filler material might make the elevator flutter. It would take some
paperwork to make it legal, too.

--

Eric,
In this case the elevator and the shape is not just for safety but
also to maximize the performance, the airfoil was design as a
complete working unit. If there is a compromise it must be very small.
If you fly with the most optimum C of G there is very little elevator
deflection for the normal climb and speed range in a steady state and
if there is, let say -2 to + 2 deg of defection, I can tell you there
is no measurable drag penalty.
Udo