Usually if you fall below 1400 (especially solo) there's some faults in your game play. That DunningKruger effect is actually really interesting. I play with some people who are learning the game, and some guy who started around the same time has been stuck at 1400 in normal mode, but he doesn't know why. I watch a lot of his game play when I'm dead or even when I lane with him, and he makes some really poor decisions in the laning phase that gets him killed. Once he makes another poor decision (usually the same mistake twice), he'll just get even more mad thus playing like shit for the rest of the game. At least he admits he is pretty bad at hon, and so do I.
I agree, and argued that one person can fuck it up for everyone, but mistakes that can be fixed can turn sometimes loses into wins. Sadly, if you are doomed to play with BR's every game, then you might be shit out of luck.