How would you arbitrate when both parties have multiple successes? Say attacker has 4 successes and chooses 4 different stunts, defender has 2 successes and chooses reduce damage to just reduce total successes, which of the 2 are invalidated and which remain?
The attacker chooses his stunts first and then the defender chooses his stunts.
If the attacker gets four successes, he can choose three stunts (the first success just indicates a hit and will do weapon damage). Lets assume he chooses, extra damage, disarm and trip. If the defender rolls two successes, he can choose the decrease damage twice, one to remove the extra damage success and one to remove the base success since both of those success dice yield damage. This will also cause the attack to miss since all dice that cause damage where removed.
If the attacker with his four successes instead chooses extra damage twice and trip for his three stunts the defender if het got two successes can't make this attack to miss (he can only decrease two of the three damage dice). He can decrease damage just once (removing one of the damaging dice) and then something else like counterattack.