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You're in a low elo where having a support that falls off mid game - late game don't carry (Tahm can carry, but it usually requires top lane gold, not support gold)
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is not an every game item and in fact usually is a bad first tier pick for enchanters. It's okay on tanks, but I see you second iteming it on Soraka.
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Your secondary runes are generally iffy after lane phase.
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I can't really tell what your in game decisions are.
You seem semi solid on the champs you play other than Soraka. My only thoughts are that you maybe get too aggressive too early, and end up dying before you get tanky. If that happens, the other adc, if smart, will start building armor pen/lethality to destroy you using the gold they got. You need to delay that and only get into a real fight when you know 100% you will win..... when their summoners are dead, and the jungler is on the other side of the map. That's the challenge with tank supports: Only going in when it's 100%.
Enchanters are more forgiving. They can generally all in IF they have an out, and ranged harass.
Personally, I've never tried to main Soraka, although I've played her. Nami and Sona are just easier to carry with, and they do so more often. Heals/move speed/cc are just so much better. If a team gets Grievous wounds, Soraka is crippled, because she just doesn't have much to her kit beyond the heals. And, unless you get VERY good at hitting Soraka's Q, you're going to drop your own HP too much and become an easy target.
You also got Heal and not Exhaust on Soraka.
You also got
instead of
on Soraka (Soraka and enchanters almost always do better with Nomad's because they can't poke enough to out gold with
, and fall way behind on gold. Nomad's allows you to safely lane and almost 100% capture your gold. You can also leave it at Tier 2, where
needs to be Tier 3, if you ever want to kill minions. This allows you to build pertinent items more readily.