I wasn't talking his later career. We were talking his original approach, in 73, and before. In later years? He suffered from arthritis. Had to change his approach. He wasn't happy bout that. But he was a pro, and never settled. And if he complained later about his ability to hear? How do you think that dude woulda dealt with it back then? That's right. The "Ox" (an animal KNOWN for it's strength) woulda got pissed, got bigger, got louder. And beat his strings. He was known for that. Back when.
You're missing two key points. First, he would turn the treble way up on his amp - at least on stage. Second, Entwistle complained that engineers never got his sound onto tape. They changed his tone to have more bottom end (which was a wise move).
The older (and deafer) John got, the worse his tone became. It's really apparent in his later solo work. He morphed into an over-processed noisy tone. He seemed to tone it down a bit when back working with the Who, and much more so on the 1995 Ringo and 2001 Abbey Road tours.