AVX's website gives their side of the story on why their coaxial compound is better. Your comment about the added complexity and weight penalty of two pusher props (or fans) versus one is correct, but the weight penalty is probably not significant. The benefit of using two smaller pusher fans is that they can be located well off center and up, which allows a rear fuselage ramp door.
One thing that I suspect all of the JMR competitors have considered, both for the tilt rotors and compounds, are variable speed drivetrains. In the case of AVX their design has small forward wings. So at high cruise speeds it appears they might be planning to slow the main rotors and use the wings for added lift, while diverting a greater percentage of power to the pusher fans. Sikorsky just stated that their SB-1 JMR design will use a T55 turboshaft engine that will be modified to allow a wider range of operating speeds (probably something like 85% to 105%). So it appears Sikorsky also plans to slow their main rotors in cruise.