That doesn't explain how I'm nearly 1500 elo playing primarily supports.
No, ranked is much more complicated than
>get paired with retards>try to carry
Typically, the more your team gets to play the roles they want, the better they will perform overall. A good AD carry might not be a good AP mid or support due to a difference in play style that's required from them. Same with throwing a jungle into the lane, or top into the jungle. Therefore, I'm not scrambling to fulfill any position unless nobody else wants to play it. And typically, people don't want to play support, so I play support. More often than not, I'll get a good or amazing outcome from that, rather than a poor one, due to people starting off happy and playing their, hopefully, best role.
I've lost more games because of people getting stuck in a position they weren't good at than being stuck with retards. And I can actively try to fix the first problem with only a little bit of effort, but the second requires much more effort than it's worth. One retard usually requires the collective effort of all of his team to stop it from snowballing out of control. If even one other position fails when there's a retard, the odds of winning go significantly down. There's too much effort behind that game for the one win you might get. And if you still lose, it's demoralizing and frustrating. It's better to accept the loss as more than likely, and play normally, than to burn yourself out trying to save yourself from one loss. That effort is better spent in future games, where skill is the deciding factor, not the crutch.