Have you performed isolation testing?
Tested and confirmed on an instance running the latest version of Simply Swords & Better Combat available for 1.21.1.

Describe the bug
Sounds produced by the legendary weapons, such as their swinging sounds when Better Combat is installed, will always play at max volume and with no directional audio, regardless of where the audio plays.

To Reproduce
Steps to reproduce the behavior:

1. Enter a creative mode world
2. Get any legendary weapon with a unique sound, and any vanilla sword
3. While flying diagonally, hold down LMB to swing each weapon. The vanilla sword sounds will pan to the side as you fly away from where the sound played, whereas the legendary weapon will remain in stereo.
4. Alternatively, use the /playsound command to play sounds from the legendary weapons various distances away from the player. Note how the sounds will always play at the same volume, no matter the distance.

Expected behavior
Legendary weapon sounds should properly attenuate with distance and direction.

Screenshots
N/A

Additional Info:

• Modloader: Fabric
• Modloader Version: 0.16.14
• Minecraft Version: 1.21.1 (affects other versions as well)
• Mod Version:
  • Simply Swords: 1.60.11
  • Better Combat:
• Environment: Tested on singleplayer, though affects any environment

Additional context
Minecraft can't play spatial audio when it is exported in stereo (I do not know why this is, I am no audio engineer, I only know that this is the case). Stereo sounds will always play at maximum volume, so re-exporting the sounds in mono should solve the issue.
I've only ever played Simply Swords with Better Combat installed, so I don't know if this issue persists when you don't have unique swoosh noises, but I'd imagine weapon active effects are similarly affected by the issue.

Wow, I had noticed this was the case and never knew why. Thank you very much for your insight!
I'll find some time to take a look at these sound files