What if, when you would normally hit the damage bonus cap, monster-family damage bonuses still boosted your damage against monsters?
Say you wear the Black Kat set, Barbarous Thorn Shield, and wield a Wild Hunting Blade. Your damage bonuses with guns, bombs, and swords against most enemies would still be capped at +6, but against beasts you would have an effective +9 when using the Wild Hunting Blade.