So, according to your post, there is a degree of correctness in both member's statements. No harm done. The Rotax C drive supports the effectiveness of incorporating the Guibo ring as an harmonic insulator. Empirical data is often more useful than calculated projections. In this case, I'll side with the C drive and applaud this new design as a plausible improvement to low-power belt redrives.The rubber ring is not truly a damper. It is a soft torsional stiffness...a torsional spring, if you wish.
Damping means removing energy from the system, typically in the form of heat. A torsional spring merely stores energy and returns it to the system sometime later in the cycle. The typical rubber spring does have a very small damping coefficient, evident when worked, as it gets warm. However, it's nothing like the damping necessary to deal with a resonant period on a continuous basis. If it was, the rubber would melt. Centaflex, a donut supplier with good published design data, actually lists what they call Pkv, maximum permissible power loss, in watts. A Centaflex A rated for 0.1 kNm nominal torque (about 74 lbs-ft, or 50 HP if applied at 3500 RPM) is only allowed 25 watts, or 0.0335 HP.
Sorry if this all seems pendant, but the use of incorrect terminology does no service to the community....and doesn't foster much confidence in the vendor among those who may possess some small understanding.