(Assuming that this wasn't in a ranked queue)
Then all of those gold and plat players probably had low normal MMR and either just goof off a lot or don't play very well. But again, I did just say you aren't going to win every game. Even aside from that, what matters in any individual game is not the rank of its participants, but the actual actions undertaken.
My point is that blaming your team is not going to help. It will not help at a diamond level, it will not help at a gold level, and it will not help at a bronze level no matter how bad you may think they are.
What is important is identifying how you can improve your game.
No, that's accurate. Jungle or secondarily mid are said to be the best roles to carry solo queue from. As a jungler you have access to all three lanes so you can choose where you influence. The jungler still relies on their team, but it's a solo queue strategy.
Mid is the same; can gank any lane, and additionally, you happen to be in one. However, you tend to be locked into the lane for a while so it's a bit less map influence.