But how could you win if you have teammates that can't also win?
If you're in a bracket where your allies don't have a grasp of basic team composition, then remember that the enemy team will also be approximately just as bad.
Besides, if you're good enough, then you should be winning most of your games anyway.
When you take into consideration that in lower brackets people are very bad at farming and the impact that items have in DotA and that creeps provide such a massive source of income, you get to ignore feed and win through superior farm.
Of course, I'm not saying that you'll win every game if you're better. It is very, very difficult to carry 4 people. However, not every lane will lose.
I mean, if you think that you're better than the bracket that you're in, then you should consistently win the lane you're in, and then let's say that one of your other lanes win while the other one loses. Then that's two out of three lanes won, which means that it's much more likely for you to end up winning that game.