I am guessing the reason this went 100 years without being proven is because it was an argument against the player piano and not an actual question that needed proving? Any competent pianist can demonstrate that they do this and it is the reason the piano became the dominant keyboard instrument.
Lol you know within milliseconds how to adjust timbre between key depress speed, sustain pressure, and pedal adjustment to get the timbre you want
I am guessing the reason this went 100 years without being proven is because it was an argument against the player piano and not an actual question that needed proving? Any competent pianist can demonstrate that they do this and it is the reason the piano became the dominant keyboard instrument.