After some failed attempts to debuff HoR boss 2, I did some testing on Beorning debuffs only to find that they apply a mere 25% of their stated value.

"-10% Outgoing Damage" from Slam results in -2.5% outgoing damage from both physical and tactical damage.
"-20% Melee/Ranged/Tactical Damage" from Piercing Roar (Blue Line) only gives -5% from both physical and tactical damage.
"-40% Melee/Ranged/Tactical Damage" from Piercing Roar (Yellow Line) only gives -10% from both physical and tactical damage.

Compared to Burglar:

"-10% Tactical Damage" from Addle gives -10% tactical damage.
"-10% Damage" from Disable gives -10% from both physical and tactical damage.

And LM:

"-15% Tactical Damage" from Frost Lore gives -15% tactical damage.
"-17.5% Physical Damage" from Fire Lore gives -17.5% physical damage.

What gives, Devs?