there are so many fallacies in this statement, including ignoring time, ignoring level growth, ignoring positioning, ignoring spell level order, ignoring mana costs and so forth. i don't even know where to begin.
soraka is actually less useful after laning phase due to the nature of ap largely being frontloaded burst and the risk required to apply starcall stacks
you are totally ignoring the MASSIVE ARMOR BUFF on her heal, which is really her largest contribution late game imo. said armor buff is even better now that hp stacking is a thing--resists are less common and more expensive overall, so soraka got indirectly buffed to some degree by the changes
I did not ignore time, the whole argument was time. The 20 second cooldown of Astral Blessing against the 6 second cooldown of Glitterlance. At lv 2 this gets even worse, because Astral Blessing is still Rank 1, while Lulu now has Help; Pix too. I'd like to see you go from 1~3 in 20 seconds in normal circumstances. If I 'ignored' anything, it's that Glitterlance can miss, but hey, Glitterlance can also hit both targets, and I didn't assume that.
And 100-0 is not hard in botlane. That's the entire aim of any lane with Leona, Blitzcrank, and to a lesser extent, Taric and Alistar. Draven can kill easily pre-6, as can Miss Fortune, Twitch and Graves. Sona is the squishiest champion in the game, and Soraka is up there.
I am not ignoring the armor buff on her heal. It also only lasts three seconds. You just wait it out, and bam, 17 seconds of useless Soraka. Meanwhile, as Soraka gets levels and CDR, the armor buff gets larger, the heal gets larger, the silence and mana restoation both grow and Starcall shreds more. With CDR she can do all of these drastically more often as well. Soraka is a lot more effective when she can throw out a 350 HP heal with 105 armor every 12 seconds as opposed to 20, with 70/25, and throw out a 2.5 second silence every 6 seconds as opposed to 1.5 every 10.
And that's ignoring Wish. You know, 2,200 burst healing at max rank. That doesn't even exist at pre-6. 2,200 burst healing at max rank is insane and teamfight turning.
As a Zyra support player, this is what happens when I fight a Soraka:
I land an early snare. The damage from me and my AD forces Soraka to heal. We back off because of the armor buff.
12 seconds later, another snare lands on Soraka because she has no evasion, trash movespeed, and didn't start boots. Soraka dies because she has no heal, and is made of paper.
This applies to Leona's Xenith Blade as well.
Soraka also struggles to cope with poke lanes like Caitlyn/Lulu, because she can't keep up with the damage.
She can't fight burst lanes.
She can't fight poke lanes.
She's pretty much useless after the first three seconds in all-in situations.
If a gank comes she's useless, be it ally or enemy, unless someone dives and she can armor buff them.
Meanwhile, in teamfights, her passive is more effective due to more targets, her armor buff and passive are more effective due to larger HP pools, she can use her heals more, she has far, far larger heals, she has wish, she can spam silences a LOT more.
Soraka is multiple times better in a teamfight than in lane. In lane she is undoubtedly the worst support atm, besides maybe Karma. MAYBE. Karma has more ways to save and aid her ADC than Soraka does earlygame, with her shield, heal, and speedbuff/slow, as well as some burst.
Honestly if I see a Soraka pick right now, I just go hyper-aggressive and take advantage of the 17 seconds it's a 2v1 lane. Things snowball quickly after a couple of sets of 17 seconds of 2v1.