I like Soraka too man. It's okay if people call her broken.
The reason why she's considered, by some, to be broken at the moment is because of grevious wounds. Before preseason started, basically any time you dropped below 40% health, you couldn't get healed at all. You always had that little thing above your head. Now that Grevious wounds only works on self heals, Soraka is extremely strong. It's made it much easier for soraka to throw her ult out and heal for a LOT of health to everyone if they are low, and it also means she can literally sit there and heal a tank and make sure he never dies.
Yes, she does 10% true damage to herself every time it is cast, but by the time that becomes a potential liability, aka when there is a chance of you being dived on, is when your Q is healing for a lot of your own health, and the other team is grouped up. Soraka makes siege and poke comps insanely strong. My last game as Soraka we spent a good 5 minutes siegeing their mid inhibitor turrent and literally every time one of them came out of base to try something, whoever they focused was healed back up instantly by me. Every time they poked someone down they were healed up, every time I was low I spammed Qs and my talismen regen made sure I had full health so they couldn't even poke me out and send me packing. Our ADC was draven so it wasn't like he could poke the tower during waves safely against an enemy annie, so we got that tower basically by letting minions hit it. And my ping was 250-300 at the time. I seriously couldn't quick reaction anything, but I was still landing Qs on people at my mid silver-low gold ranking. Her Q is just an insane skill.
Another reason is her kiting potential with her ADC. It's really not that hard to spam Qs and Ws and heal yourself and your ally as you run away until you get to a point where their stutter stepping and your Q spam means all the sudden, you're getting chased by 1/4 healthed enemies while you're full. They you just turn around and wreck them after silencing them with E.
Her Kit just has so much rage inducing stuff in it, its obvious that some will call her broken. Right now she's just in a strong spot is all. Probably THE strongest support in game at the moment. Basically any time you're at a point where you are saying "She's easy to counter! All you have to do is dodge her stuff!" about a champion, the champion is considered over powered by many. I think she will be relegated to 2nd string once Riot buffs Grievous wounds again. Yes, wish removes it, but it's like a 70 second cooldown with max CDR, not exactly spammable.
This is preseason, expect lots and lots and lots of Salt from many players about how something is Broken. Riot will do something about it. It's really only a matter of time before our tank and crit meta becomes an AP assassin meta, or a evelynn meta (plz rito have mercy), or hell, maybe Taric/Urgot will be all the rage again.