Matt, maybe you are overthinking this ... or maybe I am underthinking it. Whatever. But here's how I see it ...
Let's set the issue of habituation aside for just a minute, OK?
100% of people with LOUD tinnitus would prefer it to be less loud. Now to be honest with you, I do not have a reliable and verifiable double-blind randomized prospective placebo controlled study published in a juried scientific journal to support that statement. I'm just going to go out on a limb and say it, OK? And if anybody disagrees with me, then whatever they're smoking, I want a hit. So I'll say it again: 100% of people with LOUD tinnitus would prefer it to be less loud.
Now the reason they want it less loud is because louder tinnitus tends to be more bothersome than tinnitus that is less loud. I hope we can all agree on that as well.
On the other hand, there are people with less loud tinnitus who are incredibly bothered by it. That you will just have to take my word on. Would they be more bothered if their tinnitus were louder? I suppose so - but that really hasn't been formally studied either.
Now let's look at TRT for a minute. You don't do TRT unless you are really really bothered by your tinnitus. I mean, TRT is by and large a rather costly undertaking - you don't do it "just for kicks."
So the people who choose to do TRT are those who are really really bothered by their tinnitus - regardless of how loud it might be. And the concept of being "bothered" by tinnitus all goes to reaction, which is what TRT is 100% about - reaction.
OK. Whether you are really really bothered by very loud tinnitus or really really bothered by not-so-loud tinnitus, the success rates of TRT (i.e., becoming less and less bothered by your tinnitus regardless of how loud it is) are pretty much the same.
Would TRT take less time to be successful if you had softer tinnitus that really really bothered you as opposed to louder tinnitus that really really bothered you? I suspect that the answer is no - because the sound therapy component of TRT is the great equalizer in that regard. But as I said earlier, I do not believe it has been studied.
Should it be studied at all? Well that depends. How much money are you willing to divert from research for a cure to research that looks at whether people who have less loud tinnitus and are miserable take less time to succeed in TRT than people who have louder tinnitus and are miserable? For me, I personally wouldn't divert a dime from research for a cure. TRT, CBT, NTT, TAT, PTM, and the whole alphabet soup gamut have been studied enough as far as I'm concerned.
That's how I see it, anyway.