We went with a grab damage increase because we were looking to buff him at higher elos where he has been struggling. The LoLPC team recently did a similar buff and it had a large impact to high high elo winrate. So this felt like something we could try, with that high elo goal in mind.
We didn't want to change his mana cost because mana buffs tend to be stronger at lower elos where players are spamming skills more often.
I do agree the mana cost on his grab is high, this is intended because of the amount of power behind it in the early game. I recommend getting fimbulwinter as his first item, it is highly underutilized by the player base. It gives him survivability (health, it's shield, and from his passive mana shield), solves his mana problem, and gives him a massive amount of ability haste to attempt grabs more often.