With the removal of the old stat.<criterion> scoreboard criteria, the new ones seem to be a bit buggy. Specifically, the change of stat.damageDealt over to minecraft.custom:minecraft.damage_dealt isn't tracking the proper damage values.

To test, simply create a scoreboard objective of type minecraft.custom:minecraft.damage_dealt, show it in the sidebar, and punch something with a bare fist. It logs a damage score of 10. 10 damage would be enough to kill a pig or a cow with a single punch, and obviously that doesn't happen; 10 is much higher than the actual amount of damage dealt (about 10x as much).

Something isn't working right here...