The big picture is: sadly we don't really have any way to objectively measure hearing quality and its improvement due to hearing aids. We can push buttons whether we hear tones or not. We can count understood/misunderstood words. But the results don't have clear relationship with real-life hearing situations. For example, in my case, in silent room tinnitus appears which interferes with testing. And sometimes I hear better, sometimes worse.
Unlike vision, it's very hard and time-consuming to test with any repeatable/reproducible patterns, or to accurately explain to another person problem with quality of the sound.
Also, the hearing aids market is very tightly controlled by oligopoly of manufacturers and doctors. There is no way to self-adjust them. I'd very much buy user-programmable BTE package capable of 80 dB gain which I need for some frequencies. But there is plainly no such thing available without any strings attached. I have played with jackd under Linux, too, don't remeber clearly but it was problem to set the equalizer with 60dB differences.