Take into account camera distance to sound effects too. The further back you are, the quieter it'll sound. But you are over exaggerating I feel like since the skills themselves are obnoxiously loud... Also I wouldn't say "it's meant to be heard", since everyone has a variety of headphones, audio outputs, and so on that would change this concept. That'd be like saying a song is supposed to be heard with 100% bass, 100% volume, etc and it ends up bursting your eardrums and not sounding like the song itself. Those settings are there to accommodate the user, when I have everything at max... I can still hear myself all too well, but it does blend into the crowd BUT that also happens on any job you play as well. That's what happens when your party consists of loud sounds and your own sounds are equally as disorientating with everyone at equal volumes/distance.
This is also assume the sounds we had were all just one sound file in itself. When studios make audio, they are playing with multiple files at once they put together to make one whole skill. They make the boom of an explosion, the sounds of mechanisms working that may be the sound of a jar of screws being rattled, they make the thin slashing sound a sword makes by scraping metal together. Each of these is recorded individually and put together by the end of it in a program. All they would need to do is go back to the original steps of their audio with this job, and take the audio portion that was "the boom" of each skill, and raise its volume, which is definitely do-able with audio software.
I'm not at all saying anything that would be individually done by our hands or in game. I'm asking they take what we originally had for SFX, and adjust the thing that people had an issue with, the explosion half... not the sword slash half. Which is very do-able within their realm of development. This wouldn't even be relevant to game code, they'd have to modify the sounds they started with from the get-go, complete the sound file for the skill, meld it all together, save it, and then shove it into the game in a patch.