Jungle is the only viable solo carry role

In true solo queue (playing alone) jungle is your best and only option of having control of a loss or a win in your hands.

Provided you play very well and very consistent, if you lose that game as a jungler, nothing you could have done will win you the game.

In a game where the worst player loses, the only way you can help alleviate that disadvantage is by trying to dampen the advantage of the other players, to bring them more on the bad players level. That is your only chance of winning the game.

In solo queue nobody rallies around the fed player. They are too busy being 0/4 thinking they still have the mental capacity to make decisions or attempt plays even though they have clearly shown they are not capable of doing so. That short stick is going to be your downfall whether you like it or not.

That's why jungle is the only viable role. ADC is a strong role, but if your short stick is another lane then you're screwed regardless. Doesn't matter if you got 6 kills in lane, if they CHOOSE to play terribly then you arent winning. Period. Jungling in mid-low elo is less about getting your lanes ahead, and more about bringing the enemies down. Your teammates are not reliable, and more often than not a hinderance, so them being ahead is rarely going to help you, wheras the enemies being weaker will.

Here's an example. Lets say the mid laner is 5/0 from the lead you gave them. Sure the midlaner might be 0/4 now, but the other lanes are still capable of making a fight against them. So if you make every lane 0/2 instead, you are far more likely to create a team lead the enemy cannot come back from. As a weak enemy is weak to everyone, but a strong ally is only strong to one.