So what you are saying is that we should make a client side modification that helps us distinguish these?
To be honest there's nothing stopping you from editing the different damage sound files yourself.
For example, going into Jan's sound folder. You could record yourself saying "JAN ABOVE 75" "JAN ABOVE 50" etc, for each sound file. That's if you wanted to barebones it.
There was a pug mod pack in the AU community we used around 2006/2007, It replaced every model in the class table with a default skin, (All heroes were Lando, All sith were Jerec, etc) It also had custom damage sounds, one of our community members was a voice actor who edited all the files with the example I just gave, although it was a bit more flushed and toned. For barebones competitive play it was pretty good. I wouldn't use it in regular open play though, gets a bit chaotic outside of the usual 5v5.
Play the mod long enough you'll memorise all the models damage sounds anyway, although it is a bit harder now days with the increase of models that are being added and changing old models sound files. I only recently played and realised some of the wookiee's have new sounds.
Anyway, that's what's great about a mod, you can change and edit almost anything you like in it on your side of the screen, models, map textures, weather effects, sounds and the UI.
Model sound files are located inside, zz_MBModels