The Placement of Tonearm Counterweights

Big problem however is - no matter how good a prospective vacuum, periphery ring and/or clamp holds down the record and tries to achieve "flatness" - the record in itself is far from flat and the journey of the stylus through the groove is a constant high speed drive through a hill and valley B-road. There are hundreds of small mechanical dips and peaks during the 20+ minutes of the record side.
Each up and down works in a most unwanted way hand in hand with gravity and the moment of inertia.
The dynamic drive of the cartridge's stylus guided by the tonearm through the groove seems not that big task when you look at it displayed on a high-end TT.

If you look at it through a microscope and see the poor mechanical periphery conditions of the "track" and the many unwanted movements it gives quite a different impression.

Part of the reason why pivot tonearms with longer effective length and/or dynamically balanced mode have their advantages to minimize the dynamic-mechanical problems induces by the inherent problems of the record itself.

If an arrangement of dual counterweights placed front and back of the pivot point is entirely decoupled from the arm wand and offers a wide enough range of adjustment for an exact match of tonearm inertial mass to cartridge compliance, then it is possible to separate the problem of dynamic behavior of inertial mass from other problems related to arm wand length. The optimal wand length can then be dictated by the most significant variables. Having separated out the problem of effective mass (and also barring obvious warps from the discussion) how much vertical angular deviation is induced by a short linear arm as compared to a pivot arm? The vertical geometry of both types is of course intrinsically flawed, but is the actual difference in vertical geometry between the two significant as compared to the combined variables of horizontal tangency error, arm tube rigidity and resonance? These last three are all areas in which a short arm has advantages.

As the thread subject was the role of inertial mass, it is interesting to separate that issue from the others.

I can't understand what benefit completely decoupled counterwieghts could function. They would have to exert a force on the arm, in some way to be effective. I have to ask what the most ridgid structure would be? I understand the shorter the better so lets effectively eliminate an are beyond the slide for a cartidge to run arm as in the linear tracker.
Isn't the usual damping used on the stylus enough to maintain the effective downforce to track the groove effectively despite some inevitable vertical deflections. Why not extend the stylus beyond the pick up coils and attach a vertical gas filled shock absorber. WTF do I know but could the MC type cartridge still function with this restaining mechanism? Should I patent it?

"Decoupled" was perhaps misleading. The idea is to vary vertical effective mass using a system other than the traditional relationship between arm wand length & mass. Freed from considerations of mass, the wand can then be optimized solely for rigidity and low resonance.

Fixed mechanical damping as engineered into a cartridge suspension operates on the combined mass of cartridge and tonearm and the cantilever spring rate as a third variable. If all three variables are tuned, then perhaps the stock cartridge damping is sufficient. However in the real world external damping probably should be added. The idea of a gas-shock is a good one if it could be miniaturized and variable. As in a motorcycle suspension, the amount of damping material is determined by spring rate and rider weight.