Soraka is too one-dimensional
and I think this limits her potential greatly.
In addition, Riot has a noted disdain for dedicated healers (rightfully so), which is why I've always been puzzled by the rework she got in season 4 that pushed her even further into that territory. Starcall spam probably needed to go because it was auto-targeted and thus unfair, but her old E had a lot of variable uses -- it could silence enemies or provide mana for allies/herself.
Why did we get rid of these? They could have been implemented in healthier ways, sure, but I think Soraka would have been much better off had Riot done that instead of emphasize the 'spam-healing' she does now. The lack of options she has essentially boils down her current strength to how soon, if at all, the enemy team buys Grievous Wounds. Soraka is now an extremely passive laning champion and is discouraged from interacting with enemies at all in teamfights, save for throwing down a silence or a Starcall when she can.
I think she needs another rework, one that goes back to her roots so we can shift her away from existing entirely around healing (it should still be a strong part of her kit) and being easier to fit in the game without being numerically overpowered.
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By picking up the coins, she can sustain her own mana and her ADCs mana all the time, leading to a lane where both enemies are able to spam their skills endlessly.
. They could also work it in ways to make her feel more "celestial goddess" like.