We assess through a variational optimization approach the optimal gain-loss profile for a non-uniform PT-symmetric coupler allowing the realization of a binary transfer function and minimizing the deviation of the total traveling light intensity as compared to that holding in a conservative system. We bring evidence that the gain-loss profile fulfilling this requirement corresponds to a non-conventional situation when light intensity is conserved in every point along the propagation distance in the PT-symmetric system. Furthermore, the optimal profile thus found corresponds to a practically important case of optical switching operation achieved with a minimal amount of amplification level. We show that switching architectures using such type of gain-loss profiles are very substantially advantageous as compared to conventional uniform PT-symmetric couplers. Furthermore, this type of optimal profile turns out to be robust with respect to fabrication imperfections. This opens new prospects for functional applications of PT-symmetric devices in photonics.