So i've been playing a lot of Soraka latetly and i believe i identified a problem with your "classic support" itemization progress versus the burst mage in botlane.
Since enchanter and support tanks aren't designed to take kills you'll likely end up with many assists and very few kills. That along with the fact you won't be CSing will make your build considerably lag behind and in essence hurt your ability to do your job effectively.
Burst mages can get kills in lane. That translates building up more items and faster than you even if you have let's say 6 assists and the are 2 kills in and 3 assists. Shut downs especially now give burst mage supports a ton of gold you won't be getting.
That means that later people start to outscale you more and more and you start not being able to heal / shield or tank damage effectively.
I experimented and started to play Klepto on Soraka and i found that i can keep up with supports that can take kills much better, itemize and scale more effectively to shield / heal damage and buy some necessary survival items to not blow up in milliseconds.
Also because i give almost all of my kills to my ADC they can scale much faster too and actually carry the game. I know many people have said about enchanter and tank supports being meta again will help the ADCs.
Leona for example can be a lane bully but as she doesn't get access to gold, she starts to get irrelevant pretty fast as her tanky itemization starts to lag behind as the game goes on and you end up exploding like a tomato in every team fight after you engage.