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.