Hey bud, I had the same problem as you and made a few posts on it. I was Diamond 1 last season and this season the highest i made it to was Diamond 4. I still struggle in bronze, silver, gold, and plat when i play on smurf accounts. Games feel so one sided and like coin flip games. You can go 10/3 in top lane while your support is 0/12, adc is 0/9, mid 3/8, jungler 1/6. Then youre forced to carry the game and win.
For the most part, the best way I found to win these games is to keep afk farming. Get 10+ cs/m every game and youll see yourself climbing faster. This is because everyone is so kill hungry, they will want to group as soon as possible. This makes them lose out on overall cs because all 5 enemies are in mid lane, the lose out on Minion exp and jungle camps. Take advantage of this by farming side lanes, pushing them to their towers, then take scuttle crab as soon as possible, then jungle camps.
Doing this will get you 2+ lvls above everyone else in the game. This is where youll be able to just 1v3 and be able to solo carry, you out damage smite so you can steal baron, try it and let me know how youre doing.
If getting 10+ cs/m is hard for you, go to practice tool and practice there. Once in practice tool, buy the normal starting item and just practice last hitting minions for 5 minutes. Once the 5 minutes is up, reset the practice, then repeat. Once you get about 40+ cs at 5 minutes, add a bot to the game and practice there. Once you get 40+ cs at 5 minutes with the bot, add a bot again but this time poke the bot while also getting cs, dont use abilities on cs either, you want to use that on the enemy champion in lane. Only use it to secure a Cannon minion or if youre about to miss 2+ cs.