Notice I was speaking of the Brahms in particular. Many of my young students generate considerable power with well executed arm weight. But lets get realistic here. I recently saw Bronfman (a rather large man) play Prokofiev's 2nd concerto. Now, I'm not a huge fan of sheer bombastity, but that 1st movement cadenza was HUGE! Our precious Helene could not dream of generating that kind of sound. So though I am near the top of proponents of arm weight, there are limits. So yes, I was pleasantly surprised to see an elfin female play the Brahms 2nd concerto, as she did.