The Djinn Spirit pets are working as designed. The +25% Damage is visible in combat. You're looking at the stat bonuses that it (also) provides (shown by the green + signs).
It works like Blood of the Beast and other elixirs. The speed, luck, and bonus damage are not displayed as core character stats because they are 'bonus' effects.
Give it a try in combat! And... Happy Valentine's Day!
Bookmarks