IMHO you have got this all back to front.
The high horizontal H and low vertical V compliance of the LT arm is actually a huge advantage, and not at all the crippling problem that you describe.
The fact that a pivoting arm cannot separate H and V compliance is in fact the inherent weakness, not a strength.
Saying that the cartridge suspension compliance is the same H and V, and so the arm needs the same “to match the cartridge”, ignores what this is all about.
It’s all about achieving target resonance frequencies that won’t cause oscillations when the stylus encounters warps (vertical, up to 10 Hz, ideally undamped/steep slope) and eccentricities (horizontal, 1-2 Hz, ideally smoothly damped) in the record. These targets are very different in the V and H, hence the ideal effective mass is very different in the V and H, by a factor of 25 to 50.
Impossible with the pivoting arm, which is stuck with a factor of 1, so they just pick a rough compromise target resonance, somewhere in the middle*.
Fully achievable with a LT, because the H and V effective mass can be individually tuned. Even the different H and V dampening targets can be achieved.
Even if an effective mass H/V of 25 to 50 is impractical, a factor of 10 is still 10 times better than a pivoting arm.
cheers
* [Your claim that is *has to be* somewhere in the middle, and that the compromise point is perfect and should be constant, is exactly wrong. The fact that PL makes a similar claim is not good for his reputation.]