I feel like this is a menace at lower skill ratings and virtually useless at higher skill ratings.
Good players never let themselves have more than 8k on hand even very late into the game, meaning the amount you're getting out of this item is pennies. You may not even make up its cost unless you are CONSTANTLY meleing someone, but its stats are basically non-existent.
Cool concept, but its probably healthier for the game if gave flat extra souls on kill rather than stealing souls with melees. There's a reason stealing money out of someone's pocket isn't kosher in any other moba.