The reason it is almost universally recommended to put the bellcrank pivot behind the CG on a carrier plane is simply to make the slider work better. When the slider is released, if the CG is ahead of the bellcrank pivot the nose will yaw out from simple physics. This is more reliable and less ugly than springs, rubberbands, etc.
You are absolutely correct that where the bellcrank is mounted is irrelevant except for the above, and leadout issues, and you are also correct that solid leadouts don't belong on carrier planes. It took me a while to figure that one out. I had a carrier Skyray with solid leadouts that was a horrible flying plane at slow speed. I didn't really notice until someone else flew the plane, but the solid leadouts were trying to bend back at the wing tip in slow flight and couldn't.
They were bowed back in a large arc, and since they were all different lengths the control inputs were adversely affected. Any bobble or wobble would start the leadouts "bouncing" and amplify the bobble. Cutting the wing open and installing cable leadouts did the trick, since they were able to flex right at the wingtip.
BTW, very cool planes!