Rene,
You are correct. The application of ABC reduces the opportunity for the retreating tip to stall. In addition, by also reducing the rotor's speed, compression on the advancing tip can be reduced, and this allows for faster forward flight.
The ABC operation of the coaxial and that of the intermeshing (synchropter) are very similar. If the rotors in either configuration have only two blades each, there will be a dissymitry of lift and an excessively large vibration. This is true of both the coaxial and the intermeshing configurations during forward flight. In your coaxial example, you have the two blades on each rotor advancing together. As you say, this will give lateral symmetry of lift, but as these advancing blades approach the nose they will create a longitudinal dissymitry of lift. Changing the azimuth of blade crossing will change the moments (more or less pitch or roll) of the vibration but it will have fairly little effect on reducing it.
The actual coaxial ABC and the two conceptual intermeshing ABC helicopters have three blades per rotor and this reduces the dissymitry of lift considerably. It appears that there is still a rotor-induced vibration, at a level slightly higher than that of a single rotor helicopter, but future higher harmonic control and/or individual blade control should make it insignificant.
If you wish more detail, you may find the following pages of interest;
Sikorsky ~ XH-59A ABC
Advancing Blade Concept (ABC)
Lateral Dissymmetry of Lift
Dave J.