From what I observe of childhood hearing, his ear as a child must have been extraordinary and, just when he was coming into adulthood, the realization that he was losing his hearing must have intensified his awareness of precisely that child quality of hearing.
I have a student now at the age at which Beethoven became aware of his impending hearing loss, a young man whose ear is entirely uninhibited and entirely accurate.
From his precision I catch glimpses of how Beethoven must have heard the piano and of the origins of some of his works for the instrument. Nothing theoretical. Pure ear.
It is humbling to recognize the extent to which theory and efficient technique only mask the reality.