Maybe something like this:
<GameModifier>
<ModType>Unit</ModType>
<Attribute>AdjustUnitStat</Attribute>
<AttackStat>UnitStat_Attack_Blunt</AttackStat>
<Calculate InternalName="TgTpCt" ValueOwner="TargetUnit">
<Expression><![CDATA[[UnitOwner_GetTroopCount]]]></Expression>
</Calculate>
<Calculate InternalName="Calc" ValueOwner="TargetUnit">
<Expression><![CDATA[[UnitStat_Attack_Blunt]]></Expression>
</Calculate>
<Calculate InternalName="Calc1" ValueOwner="TargetUnit">
<Expression><![CDATA[[TgTpCt]*[Calc]]></Expression>
</Calculate>
<Calculate InternalName="Value" ValueOwner="TargetUnit">
<Expression><![CDATA[[Calc1] * -0.75]]></Expression>
</Calculate>
</GameModifier>
I am not sure if this is 100% right, but maybe like this
Now maybe this could be applied to a blood trait and just give it to all races or perhaps this could be put directly into coreunitgroupingtypes, not sure if that is possible though.