How does soraka fare against other supports in a teamfight?
Even as the game nears the end, thresh and blitz have their hook to make a play, morg has her ult stun, annie has her ult stun, even tahm has his devour save the adc. Except for healing a single person with w (and team with ult), what cc or game changer does she bring? Her E should never hit root a champion on its own.
and you will root someone. Root someone and you win the team fight. You should win anyway, since your team never leaves full health.