So a little noticeable immediate improvement. The existing wall is decoupled. You doubled the mass on one side of a staggered stud wall and damped that mass.
Damping alone can increase a staggered stud wall performance 5 points. You added damping + mass on one side so one might have expected a 9-11 point increase perhaps. A 10dB increase in performance would correspond to a halving of the acoustic energy.
This assumes no flanking, and walls, ceiling and floor = flanking opportunity. Given your assessment of the improvement as well as the fact that a decoupled wall was as problematic as it was to begin with points to flanking. Likely significant flanking.
The triple leaf effect that we avoid is diminished as the air cavity increases. If you can add a 4-5" air cavity you are getting out of the danger zone so your improvements will have a chance to pay off.
There are several third party certified lab reports showing performance expectations of the surface treated. However, if only 60% of the sound energy is passing through that wall, then clearly even a perfectly soundproof wall will only reduce the sound you're hearing by 60%.
All data points to significant flanking so I would recommend turning your attention from the wall itself for a moment and look at how sound is flanking around your wall. Again floor, ceiling and side walls. Pipes, ducts, in the side walls, in the floor or ceiling near the wall as well.
This assumes the damping itself was applied correctly and that any penetrations in the drywall were properly sealed, as well as the perimeter of the wall, especially behind the base molding.