> As he gets older, the activity of the hands become more dissimilar in his piano work, and farther apart
Well that can be said of many composers, even the ones we think of as "old school", like Bach. From the middle of Bach's life onward his music gets increasingly challenging and dissonant. Play some of the alto lines on a flute and it's indistinguishable from bebop to a layperson's ear. Seriously crazy shit.
Also, even though Bach was a also string player (and probably an expert one, because he could play Bach pieces ;) some of the published works end up with errors that are hard or impossible to play. This can’t be attributed to deafness. As with Mozart, Bach and many other composers (maybe not Haydn), Beethoven seems to have got bored with his older styles and kept moving aggressively forward.
"From the time I was a little girl, I have been fascinated with how deafness affected Beethoven. If you look at his piano sonatas, in that first one in F Minor, the hands are very close together and the physical choreographies of the left and right hands are not that dissimilar. As he gets older, the activity of the hands become more dissimilar in his piano work, and farther apart."
and
"I think it’s fascinating, too, that as Beethoven’s hands stretched for lower and higher notes, he demanded pianos with added notes, elongating the pitch range of the keyboard; he asked for physically heavier instruments that resonated with more vibration. More pitch distance and difference, and more vibration and resonance, create a recipe for happiness for a hearing-impaired person, trust me. A more dissonant and thick language, with clashing frequencies, also causes more vibration, so the language does get more physically visceral that way, too."
It's a fascinating article and people should try actually reading it instead of jumping to conclusions about it.