I tried an all-moving fin/rudder combo on the same basic design that I have used previously with a normal fin/rudder. It developed about half the yaw angle of the conventional fin/rudder, with the same planform and same total area.

A few years ago, some pattern flyers were touting quite thick vertical fins. I whomped one up from foam, and tried it in a wind tunnel. I could discern very little improvement, if any, from the thick fin, so I stayed with relatively thin fins, with about a 50/50 area split between fin and rudder. The fin/rudder combination evidently can develop, with 45 degrees rudder deflection, about twice the lift coefficient of an all moving surface.

Cessna was forced to add a slot to their all-moving horizontal stab (stabevator) in order to get sufficient downforce for landing with a forward CG. This must have more than nullified any reduction of drag that might be obtained by eliminating the hinge line.