10% for soraka isnt high enough.

Soraka's heal has an 8 second cooldown on level 1. I doubt those 80 hp once or twice per fight were the reason why you lost.

Also, when you're against Soraka, you buy Grievous Wounds or you focus on poking her. If you did neither, you're setting yourself up for failure. And if you had a tank support, you would naturally have had loads of issues going against a Soraka/Vayne bottom.

To be honest it's not as bad as you make it out to be...

• Her W costs 10% Maximum Health at all levels and additional 50 to 70 Mana (Based on ability rank)

• 60% of her kit can be countered by Grievous Wounds (Q + W + R = 60% and Passive + E = 40%) because that 60% is all heal based abilities, where the other 40% aren't.

• She doesn't really have any proper sustain outside of her R or Redemption (Her Q sustain is really weak in later stages of the game), so she will run out of health to heal someone. It's that or her heals will be less effective when Grievous Wounds is applied and she will not be able to outheal the damage that her allies take.

Just try to poke her out of lane, and if engaging, just focus her first, she's squishy and immobile.