Well, your mod is working, but I don't think the code is doing what you think it's doing. Or else you're doing a little obfuscation.
I modified your items.xml like so, just 9 damage, and still die in one hit.
<HellsJanitor>
<set xpath="//item[starts-with(@name,'meleeHandZombie')]/property[@class='Action0']//property[@name='DamageEntity']/@value">9</set>
<set xpath="//item[starts-with(@name,'meleeHandAnimal')]/property[@class='Action0']//property[@name='DamageEntity']/@value">9</set>
<set xpath="//item[starts-with(@name,'ammoProjectileZombie')]/property[@class='Action1']//property[@name='DamageEntity']/@value">9</set>
</HellsJanitor>
If I delete items.xml from your mod so it's just vanilla, still die in one hit.
ok, I've confused myself here
You
would die in one hit because of the "chain reaction" in buffs.xml:
<buff name="buffOneHitKillTrigger" showonhud="true" name_key="buffOneHitKillTriggerName" description_key="buffOneHitKillTriggerDesc" tooltip_key="buffOneHitKillTriggerTip" icon="ui_game_symbol_zombie" icon_color="204,85,0" icon_blink="true">
<duration value="0"/>
<effect_group>
<triggered_effect trigger="onOtherAttackedSelf" action="AddBuff" buff="buffOneHitKill">
<requirement name="EntityTagCompare" target="other" tags="entity,zombie,hostile"/>
</triggered_effect>
</effect_group>
</buff>
<buff name="buffOneHitKill" hidden="true">
<duration value="0"/>
<effect_group>
<triggered_effect trigger="onSelfBuffStart" action="ModifyStats" stat="Health" operation="subtract" value="99999999"/>
</effect_group>
</buff>
The trigger is applied to the player on first spawn, and the one-hit kill buff is applied any time the conditions within the trigger are met.
Quite why I changed the zombie hand damage in items.xml is completely beyond me ...