o.k. - back to the mere prosaic world of analog-highend audio.
If the rigidity of a given tonearm AND its moving mass AND its ability (if there is any ability) to transfer energy is NOT diminished by the increased length of the armpipe - then the advantage in minimized geometrical error will show off in "improved" (whatever that is..) sonic presentation.
So - if all strong points of a given tonearm-design are preserved while increasing its length - and thus decreasing its geometrical error (tangential...) - then the longer version will be the "better" version.
As with everything in our physical sphere, there is a "window" or "frame" of superior function under the given mechanical circumstances. Below 9" the error in a pivoted design becomes too large to allow serious high-fidelity sound (at least to my ears). Above 12-13" there will be very few plinth/turntables around to accommodate a tonearm of that length. Furthermore the further minimization in tangential error will be so little, that it won't show off any more in real-world set-ups.
Between 9" and 12" there is a significant improvement in tangential error and the toenarms of that effective length still do show reasonable rigidity and moving mass.
Compare the 12" to the 10" versions in tonearm-designs like the SME, the Ikeda, the Phantom II, the Fidelity Research FR60s-series. While the differences are subtle, they are there. Clear and in all the different designs of the tonearms just mentioned, they are showing in the same direction.
I like it when physical laws and geometry show their impact in analog.
Not all is myth or voodoo.
