As someone who has designed and built a hearing device, I can share what I've learned.
Just to push back only slightly. Any hearing aids, including the very expensive hearing aids I am trying are only as good as their programming in an effort to match frequency(s) of hearing loss. My Dr. of Audiology told me, there is a lot of 'art' to tuning hearing aids after a comprehensive audiology evaluation.
That much is true. An audiogram (which is the input to the fitting process) is a very coarse way to represent someone's hearing, so it is not surprising that a lot of trial and error happens during the fitting iterative process.
The other part to this is that there are standard fitting tables that determine your amplification based on your loss, and they are not symmetrical: if you are down 40 dB at 8 kHz, the HA will not compensate by adding 40 dB at 8 kHz. The tables are called NAL (and later NAL-2), but most HA brands think that they have a better "secret sauce" that they hide behind a more complex algorithm, with an accompanying software that an audiologist has to use to program the HA. That means that the audiologist doesn't really know "what happens" when they use this or that button: the button is there to represent a condition ("patient hears echo"), and the algorithm will then decide what is best to do. They are trained by the company, but the complexity is just too high to really be able to understand all the intricacies of each brand (I don't blame them).
Because of this "black box", audiologists have learned from experience using various settings with their patients, so they know that a patient complaining of "this" is addressed by pushing "that button" in the software. That is the "art" part.
I have a measured hearing deficit in the 8K frequency range for both ears. The dilemma for my audiologist is...my gain shift of about 20dB or so aka hyperacusis, increased sound sensitivity. If she really turns up the gain on my high frequency to fill in this sound loss, this noise is painful for me. Trucks are painfully loud walking outside etc.
That's where the "art" part comes in... tweaking a bunch of settings like gain, but also compression, filters... until the patient says "that's it!"... but there is no guarantee that a set of digital filters will be able to correct to a satisfactory level. Still, it's worth iterating a handful of times. At Costco, where I got my latest set of HAs, we iterated a few times by making an adjustment in the booth, and me going out of the booth for a 5 min walk around the store to see how I would feel about loudness across bass/voice/treble frequencies. I'd go back to the booth with my feedback and we'd go for another round. That can take over an hour just to do an adjustment, sometimes without a successful outcome. It can be frustrating.
Also, many HAs will offer you a button that you can use to change the program: in my case, I have to increase the amplification a bit when I'm in the car to hear the radio sound better. I have a bit of control, but not much.
Your theory of filled in high's with hearing aids as protection against loud sound is an interesting theory.
Can you produce a link aka scientific study that supports your claim? I would like to read the technical explanation behind such a thesis.
This is not a scientific study type of data. It is a product requirement type of data. The high level safety requirement is "do not blast the ear ever" (sounds reasonable, doesn't it?). That means the algorithm will not add any amplification to bands of frequencies that already have too much energy: a loud sound will not be amplified.
Example: if you have an "open ear" HA, then an environmental sound of 120 dB will not be amplified by the HA, but you'll still get 120 dB in your ear. In that sense you're not protected. However, if you have an "in the ear canal" aid, it acts as an ear plug before amplifying the sound to the ear. Roughly speaking, if the presence of that hearing aid in the canal drops the volume by 20 dB, then when it picks up a 120 dB sound, it will decide to not amplify it and the ear will only be subjected to 100 dB. It's obviously more complicated than that due to bone conduction, the fact the attenuation isn't uniform across frequencies, and other factors, but you get the point.
Brace yourself. $1000? My audiologist must think I am rich.
Mine are priced at $6,400....as in out of pocket cost.
Shop around. The most expensive ones aren't necessarily the best ones
for your hearing profile. HAs are expensive though, generally speaking, not unlike other "durable medical equipment". Costco sells the same hearing aids as the other stores (ie same brands), but they sometimes lag by 1 year in technology, and they have a limited set of options, but trade that for a better pricing and warranty.
Good luck with your fitting. I hope you find something that helps you.
Unfortunately, it is still present even after removal of the hearing aids. 
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