well, as for attacking a monster, size & race modifier cards won't increase DB damage. in PvP/WoE scenario if you attack a player and he's wearing hydra card or any other reduct gear (can be WoE gear or gear with ranged dmg reduct), OR water/fire element resist gears (ex, pasana/angeling/swordfish) it will reduce the dmg of DB or wDB.
below is the current DB formula.
[(CurrHP ÷ 50) + (MaxSP ÷ 4)] × (SkillLv × BaseLv ÷ 150) × (95 + DragonTraining_Lv × 5)% × (100 + Ranged Damage Modifiers)% x (Elemental Modifiers)%