@ConManNate making one gear fully solid would approximately double the spring constant of the compliant side, but the noncompliant side dominates the stiffness, so overall it would be a small difference in stiffness with some other disadvantages
if you make only one flank compliant, then you get zero backlash with the original noncompliant transmission stiffness, so long as the compliant preload exceeds the load torque
@seveibar I've done this before. only one side of each tooth should be compliant: meshed stiff face to stiff face, and compliant face to compliant face. you'll get the same backlash advantages with much higher transmission stiffness