The ultimate Ultimate Adventurer's info thread... :)

I think you're mixing up two skills here.

Wind Piercing = 700% dmg * 3 for UA Archers
Storm Break = 2nd Job knockback skill for Wind Archers

All that Wind Piercing is, is a heavy 700% damage attack (x3 monsters), which is kind of slowish (1080ms). But since it's 700% damage, it has the best potential to knockback bosses that require high knockback damage.

Okay, I see. I guess "The only use I can think of is knocking back bosses (600% dmg), since Dragon's Breath doesn't work on bosses" is a little misleading.