Well, I don't know. Ir doesn't give huge sustain as
, it doesn't give a powerfull slow as
nor makes you an awesome dueist as
. I could see that reduced to 2 seconds if used on an ally, as that would reduce its power against sustained damage instead of burst.
Or maybe something like:
PASSIVE: Using Smite on a monster grants you a shield that gives X Armor and reflects Y% of damage received to the enemy for T seconds. If you use Smite on a target on an allied champion both you and the ally receive that shield.
ACTIVE - On Ally Chanpions: Using Smite on a champion grants it a shield that gives X Armor and reflects Y% of damage received to the enemy for T seconds. If you use Smite on a target on an allied champion both you and the ally receive that shield.
It helps at jungling (what Tanks need), doesn't provide battle bonus so that fighters/assasins don't abuse it, and gives tanks a somewhat utility at teamfights.