My thinking is that Uni Pivot Arms addressed an issue with bearing manufacturing tolerances, materials, and quality control. I think the bearing industry has caught up, and perhaps surpassed some of the Uni Pivot Arms out there (I have a couple of very vintage Mangepan arms, one installed on a vintage Realistic direct drive that has been converted to manual, from semi-auto. It is seldom used these past twenty years, newer equipment has taken over the dedicated mono role.)
Uni Pivots have a loyal following, and for that upper echelon TT and cartridge set-up, when set up properly, may remain unbeatable for awhile yet.