The mace's falling smash attack activates while the mace is on cooldown (the sword icon isn't fully filled up after an attack and you won't do full damage). This is in contrast to a sword's sweep attack, which will never activate while attacking during cooldown.

How to reproduce:

1. Take a sword and spam-attack a mob.
2. Notice how the sweep attack does not activate if you attack before the cooldown is done.
3. Take a mace and fall onto a ravager from high enough to kill it.
4. Just before you hit the ravager, swing to the side, not hitting it, to activate the mace's cooldown.
5. Hit the ravager while cooldown is still active and you're still midair.
6. Notice how the mace's smash attack activates and the ravager dies despite the mace still being on cooldown, unlike the sword's sweep attack.