what soraka doesn't do is help your team pick the fights they want to fight. and this talk of only bads get hooked is incorrect, good blitz's create "even if I miss I can't miss" situations a la
http://www.youtube.com/watch?v=20G17K_0ghU, but that also isn't the only way to land a hook. in lane, good blitzes scare the shit out of the enemy by charging at them with powerfist on. they lose cs by running like ninnies, and if you hit them, free hook.
Never said she's bad, but lategame is her weaker phase. If I had a choice of having a equally farmed support late game blitz/ali or a lategame soraka on my team it'd be blitz/ali in a heartbeat.
ok now I see where soda is coming from. you are comparing situational scenarios; it's soraka armor and heal for stopping dives and making sure the AD lifesteals enough to survive or the initator can take that much more damage vs. ccing and allowing repositioning vs. making a pick off a group
soraka is just as weak late game as any other support, but they still do amazing things in teamfights. armor and heal is an amazing EHP boost
she can't initiate, but she can stop the ezreal's e. blitz can initiate and force a fight, but he can easily be put in a position where that is a bad idea. you rather having a blitz/ali speaks towards the situations you privilege in the late game, but these situations vary (can I turtle the stronger enemy team until the next baron fight? am I stronger than them and I want to force fights? are we fighting in the middle of the lane, in the jungle, at baron, etc.? am I trying to keep the enemy damage out of the fight long enough for our team to gain the advantage in a teamfight? or am I trying to get my team to hunker down and duke it out?)
edit: I mean, what's the point of an ali/blitz if you are getting poked the fuck down and starting fights with half health. Soraka definitely excels at prolonged siege, and in some cases turtling (though if a siege is taking too long, most teams will just run off to take an objective).
Also it is my belief that the best reason to run blitz is to last hit people with q so you punch them to death.