Too many champs is a likely culprit, and the fact you brought it up means you have the general idea.
- You're in an elo where you likely haven't even mastered beyond 1-2 champs. Yet you play like 30.
- You're in an elo where you probably can't/don't look at your own team and the enemy team and think, "How will each fight play out if people use their champs to their potential?" You likely just more randomly choose champs based on preferences, and your specific lane's tradeoffs.
- You're in an elo where an item meta/champ meta doesn't exist.
- Some champs are anathema to winning generally in low elo without a proficient duo. For example, I would never 1 trick Yuumi in low elo, simply because her teammates will lose the game on their own, walking right into 1v2's with Yuumi attached, thinking her heals/shields will save them.
My advice: Choose a champ or two in one specific role, and just play them. It's better to have two so that you have a backup if you're banned, and try to make those 2 champs play off each other's weaknesses, so that if one is banned, the other can compensate not having them.
Learn to ward.
Learn to think that Towers are more important than kills (spending 40 minutes chasing kills is not a constructive win pattern)
Learn to realize early deaths are far more important to game outcomes than ANY other feature of the game, including Drakes/Barons/Towers. So don't die early! Take cautious routes, and be willing to give up some 1v1 exchanges because of the risk you might get outplayed. (I'm not saying don't fight. I'm saying learn to tactically retreat, possibly toward an ally, and turn a risky situation into a saved life, or a 1v2)
p.s. I looked over your account, and you generally have very low kills, and substantially high deaths. Many games suggest you spend more time cowering than fighting, because you don't trust your own capabilities.
You also average 4 cs/minute, vs an elo that averages even 6 cs/minute, and smurfs who average 9 cs a minute in your elo. You need to better establish your minion gold income, and not be as scared/tilted to contribute to team fights.
I'm not trying to insult, but you're at an elo where 15-20+ kill games should be common if you are a proficient player. You usually get 3-6 kills if you're lucky. You're usually not why your team lost, but you definitely aren't why they win, either.
As a support you rarely even upgrade your gold trinket. At least T2 it. T1 doesn't finish gold quests, get wards, or give good gold.... Your goal should be a 8-10 minute gold quest and a T2 upgrade as soon as you are able to.
I think gold income is your #1 issue. It makes you play less. It makes you spend more time farming. It makes you weaker in trades.
Too many champs is your #2 issue (and probably because I also believe that because you spam in sequences of ~ 7-8 games per champ, you generally don't pick counters to the other team or synergies to your team, which means you DO need more experience with more champs still.
If you can get gold incomes up, while bringing the number of champs you play down, you'll probably climb.