Dougdeacon has articulated a far better answer than I could, and I very much concur with his final phrase about the devil being in the detail. I think that arms such as the two Caliburn ones (Cobra and Copperhead) are both 9 inch uni-pivots which illustrate that execution is the most important thing. I personally was a bit ham-fisted when I first ever used a unipivot moerch and was put off as a result. Some say gimballs are more evenhanded overall, it may be due to not being able to pivot in the azimuth.
Philosophy: Bearing vs. Unipivot
I was looking at the VIV Rigid Float arm on AG today, and a couple of things struck me. Obviously, the primary one is that there is no arm offset on this arm, no overhang, no need for anti-skate. But, secondarily, I can really follow Ivor Tiefenbrun's thoughts on the Linn turntable: any relative motion between the stylus and the groove harms the sound. Stable bearings, whether gimballed or not, solve this situation. But there are so many unipivot arms out that are well-thought-out and well-regarded, including the aforementioned VIV.that there must be something more going on with them than there used to be, because there just HAS to be more relative movement with a unipivot arm than one with bearings. Someone please educate/enlighten me...