Hero needs atleast 20 minutes of farm, which is no fun to play as 4 vs 5 and after that it's not garantee that he will carry, because he can just "wants to farm more".
Make him some kind of inquisitor which will burn enemy witches for using spells nearby.
Here is my rework.
AGI 16+ 1.5
Q. Burn Heretic.
Enchants a target, dealing 50/100/150/200 damage providing vision of them and Burn* effect for 4 seconds if they cast a spell or if the enchantment timer expires.
Burn - dot 15/20/25/30 damage and 10/15/20/25% slow.
Cooldown: 24/20/16/12 seconds. Mana cost: 75/90/105/120
SOTM Effect: Turns Burn Heretic in to Burn Heretics making in an AOE spell.
W. Holy blessing.
Removes debuffs and disables from the target friendly unit, and grants bonus 10/20/30/40 movement speed and 30/40/50/60 health regen for a short time.
Duration: 5 seconds. Cooldown: 16/15/14/13 seconds. Mana cost: 110
E. Master of mantra.
Passive effect: Magebane proves he is the master of the flow of Magic around him, granting him 2/4/6/8 Magic Armor.
Active effect: Magebane activates aura which causes nearby enemy heroes to lose a 1.25/1.5/1.75/2% of their max mana every second, and Deals Magic Damage equal to 35/50/65/80% of Mana used when they cast.
Duration: 10 seconds. Cooldown: 30/25/20/15 seconds. Mana cost: 100
R. Iron Maiden.
Traps targetet enemy in Iron Maiden for 2/3/4 seconds dealing 70/100/130 damage per second and increasing incoming damage by 20%
Cooldown: 100/90/80 seconds. Mana cost :150/200/250.