I was all for old Soraka, but I'm still a big user of Soraka. Going as gradually as you said would have been a complete waste of time. Riot didn't like how she played (she could poke and silence an enemy the entire game from a safe distance). The cooldown was short, so they added a mana cost, but that wasn't enough. So to put more skill into her, they gave her an AoE Silence. Though easy to land, is not guaranteed. Then starcall was also an issue with pushing lanes unintentionally, so they fixed it. Then they aimed to make her the "healing" support again because she was getting outdone by Sona and Nami, so they drastically reduced the cooldowns, but added the health cost/
I have not had a game yet where her health cost was the reason I lost, I've played her only about 25 times, about 12 in ranked. I think it's a tad high, but that could be reduced to 8% instead. The fact that her heal can go to 1.4 seconds late game is absurd. And her ult now removes Grievous wounds. No other champ has that ability.
She's in a good place.