Soraka can heal 60k+ damage out of 250k
http://i.imgur.com/xwCzp8v.jpg Why is one champ able to play the role of jesus and negate 25% of an entire team's damage?
If Soraka is on the opposite team, your team is literally stuck with 2 supports, the original support and the ADC since soraka's heals turn him/her useless. http://i.imgur.com/KMrmGI1.jpg This champ with no weaknesses with high rewards is breaking the game's balance.

has by far the most balanced form of team healing in the game.