I feel like blunt damage would have made more sense for MCH.
So MCH dmg type is piercing, but I feel like blunt would have made more sense both from a lore and gameplay standpoint.
For lore, most of the guns we use clearly look like muskets. Muskets fire ball bearings which would be blunt, not piercing rounds like are used today.
As for gameplay it would have been nice to have MNK buff another DD other than itself and this way BRD would be buffed by DRG and MCH would be buffed by MNK, giving both support DD's a synergy with a different melee DD.