Mercedes Balance Analysis

If you even bothered to run the skill data through Google Translate, you'd realise that the defense negation is a debuff to the target and not a true "party buff". Joe refers to it as a "bonus...for the entire party" because it is indeed that; it boosts the damage of the entire party, except not because it gives everybody a 100% chance to ignore defense by 20% for 15 seconds, but because the victim has its defense reduced by 20% for 15 seconds.

My actual point was I was tired. Legendary Spear doesn't state itself as a buff for the party, but since it is a debuff for a monster, it should affect other users attacking it like Threaten. Unicorn Spike states it works for party members in its own description to establish that it is unlike Advanced Homing's status effect.