I have realized that it does nothing now that dynamic damage is added.

Hello!

• Weapon swings hitting multiple targets now deal reduced damage (the maximum damage penalty is 50%)
• The more enemies you hit the less damage your weapon swing deals
• To unleash the full potential of your weapon swings, and always hit full weapon damage against all targets, you now need to have Sweeping Edge enchantment
  (All related values are configurable in config/bettercombat/server.json5)

I recommend Discord for QnA.