So Soraka is hard countered by Grievous Wounds...
But with the addition of the new support stat (that still doesnt have a simplified name yet) a full build Soraka's heal will be increased by roughly as much as GW decreases them, evening out to her healing as much as if you hadn't bought it. Considering how well she synergizes with certain tank items (
) on top of it , "just kill her first" doesn't exactly work either. So what beats her now?
which is both Sightstone and Gold gen item in one. Not to mention if she gets 5 items + boots she wont have slots for control wards. Her team needs to be so far ahead for her to be brave enough to risk so much vision for those items. And if she is so ahead then her heals dont really matter that much.
or just more AP for better heals 
counters Soraka until she can build multiple items. As late game damage is measured in 1000s by the time she has those items her allies are getting blown up in 1-3 seconds (often less) making her heals useless. Soraka has late game impact by the placement of her E which has a very high CD. If you lost to a soraka its because they got ahead for the mid game. She is one of the best champions for snowballing because her healing prevents you from getting kill and catching back up. She can be countered with a single item and if you make it past her mid game her heals will rarely make a big difference unless your team has low late game damage. Soraka is a great pick against a tank heavy team as their damage is low so her late game will be very good. Against 3+ high damage champions her healing is easily overwhelmed in late game and she might have time for one W + R at those damages (weaker too due to GW, you can work math and a Lulu E + R is far superior to saving allies as it can't be reduced by GW). Building her tanky only makes her healing weaker.
plus the right rune set-up lets her push 3k hp with slightly over 100 Armor and MR late game and still invest in +30% heal power. Just drop your no-longer-gold-efficient starting Coin item for a stats item later on.