I am almost sure Rito somehow locks "carry-players" against feeders. I played in S5 for a long time, racking up ridiculous killscores every game and winning every game. However, as soon as i got S4, one guy (toplane usually) would consistently feed 10 kills (not even lying) to the enemy Jax before 10 minutes. I dont care how good a Mage you are, even Plats/Diamonds gets shit on by an overfed Silver 4 Jax.
The thing that helped me out was a Diamond smurf on my team in a game, that asked if we should smurf together - he was sure i was at least Plat. I told him i wasn't smurf but we still duo'ed to S3, and i solo-climbed super fast to S1, and soon thereafter to G3 - it seems like the system had run out of Wood 5 players to put in my games. With fair teammates, i am Gold 3 at least, and was also close to that skill level when i was S5.
Really, my advice would be duoing with a Diamond smurf. I have seen ur games, and you will be able to literary 2v5 the enemy team. Climb to mid-Gold and try solo again
Else, try to play Tahm Kench top. Kill the enemy laner twice (hilariously easy vs Silvers), and then try to bait the enemy jungler to gank. You should be able to 1v2 them, and so much pressure WILL make your team get advantage on the bottom half of the map. Lategame, you dish out so much damage, but can actually 1v5 for a while, especially if u are far far ahead (4-0 cuz 2 solokills and double on gank) you will do so much dmg
Zed mid is also a great champion for 1v2's.