Considering any one element such as arm weight ignores synergy of the various functions and roles of the joints, tendons and muscles of the entire system comprising the playing apparatus. Much playing demands various combinations of "synthesizing motions" in which weight might be one of the forces, but not the most important in a particular instance, or perhaps even a detriment. When synergy is considered, the parts do not usually equal the whole. In fact, they can well exceed the whole--which leads to superior performance.
Some background to better make my point: I studied for many years with two teachers. The second one was of the Russian School, going back through Anthony Di Bonaventura to Isabella Vengerova, a student of Goldenweiser and Leschetizky. But for my purpose here, I refer here to my first teacher who had studied with David Barnett (a student of Cortot and Brockway, identified with the French School), Miklos Schwalb (a student of Erno von Dohnanyi, of the Hungarian School), and Albion Metcalf, a student of Tobias Matthay, of the English School).
For anyone reading this, Matthay should sound very familiar. He developed the method of tone production based on arm weight and relaxation. In addition to Metcalf, mentioned above, he also taught Bax, Craxton and Hess.
I mention this so you'll better understand what I'm about to say, which might sound like heresy to some. Because my first teacher got Matthay's teachings directly through Metcalf, you can well imagine that as her pupil, I got a super dose of it as well!!! But as the decades went on, it seemed to me that tone production through weight and relaxation was SUBJECTIVE in the ear of the beholder rather than being objective. In other words, I've become a doubter. Tone depends on acceleration of the key, which can be accomplished by pressing, striking, or arm weight, except that the latter is a handicap, not a help, in playing velocity. And I'm unconvinced that arm weight necessarily and invariably produces the most beautiful tone. (Similarly, I believe that Abby Whiteside's prescription of playing piano with the upper arm can result in some ugly sounds at times.) So for me, I no longer see weight as the hub of the galaxy of pianism. Rather, I've come to believe that the truth lies more in the holistic system and the subsystems of the larger playing apparatus, acting separately or otherwise in concert or combinations to effect a musical intention through synthesizing motions. It would be wonderful if it all were more simple, but I don't believe it for a moment.