An interesting white paper.
The ET2 horizontal effective mass can be as low as 25g less the decoupled counterweight compared to the 80g Kuzma Airline.
Kuzma ignores tracking and focus's only on resonance. I always thought the target of 8-10hz was partially based on keeping it above footfall on sprung floors which is typically around 4hz.
If you examine the Shure white papers on tracking, they have found that the fundamental resonance, if not dealt with properly, causes a scrubbing motion from the cantilever/stylus assembly. This causes tracking issues and of course distortion in the bottom and its harmonics that will distort up into the audible regions. I assume this is why they came up with the stabiliser brush.
Kuzma makes no comment on the impact of high mass on tracking at low frequencies, and there is no measurement indicated in the white paper.
Even Bruce Thigpen of ET states that on eccentric records, arms with high horizontal mass will be less accurate than lower mass arms.
Bruce Thigpen has measured wow and flutter on pivoted arms versus air bearing linear tracking and can demonstrate the linear tracker has lower wow and flutter.
His argument, supported by measurement is that there is typically more wow and flutter from a pivoted arm than from the TT itself.