Because Riot can predict who is going to afk or leave... yep. Totes. (Hint: If they could, they'd be able to ban them quicker)
The ranked system doesn't change who you're matched with or against. It's the same game. The only thing that changes is the importance you put on it. Since you put a greater level of importance on it... you notice the things that go wrong more.
As to the whole doing most damage as a support, that isn't that uncommon depending on the support. Supports are put in the unique position of having nothing to do for the first 20 minutes except deal damage to champions. They don't have to worry about minions. You can build up a LOT of damage by doing small amount of damage consistently for 20 minutes. As Zyra or Karma support I was USUALLY at least #2 in damage on my team, and often #1.