How to win in low elo?

So I'm currently trying to climb back to my peak with katarina, but I'm having a hard time despite the game being generous with lp. I tend to do well every time up until late game and I'm fed every game. The problem is, sometime there's like 2 fed tanks on their team. For example, the last game I played, the enemy yi and camille was fed. Obviously in late game, when they have mr, I can't oneshot them, and they one shot me instead.

What do I do in that situation? Was playing ad the right choice since it scales harder? I remember katevolved saying he would get like a 100% win rate in low elo, so I'm sure that game was winnable if I played different, but I'm not sure how. How can I play differently to where I can convert me being fed into wins? You can also assume my team mates are not the most useful in the game (no cc/damage/doesn't engage/doesn't listen to pings/feeding). I know 1v9 carry isn't something that's often done in season 16, but how do high elo players able to do that?