Currently it’s almost an anticlimactic surprise when a boss dies to damage on dodge, parry or block. (Maybe thorns too, I haven’t played thorns because I don’t like eating hits)
Suggest adding a visual tell to reactive damage so the player can see it has an effect and isn’t left wondering there the boss went.
Optionally: consider changing all reactive damage to poise damage. That way the boss is still there, but potentially open to reprisal and the player has to do something to kill it.