How to Fix Soraka
There's no way to change Soraka's mechanics for laning, but the reason she's banned is because she essentially controls the team fight. Most of the time, a team must get her or no matter who they focus, it won't be enough. And, if a team can't dive her, they'll lose the fight. So to fix that, Riot needs to adjust soraka so she can't heal just anybody at any time. Instead, she can only heal one person, and then with a 15 second cooldown, she can only heal that person. Once the cooldown is up, she can select a new person to start healing.