I agree with everything except last point. 20/20/60 rule is ridiculous, I am sure there is no serious study about it. You sometimes do better, you sometimes do worse than you average gameplay skill. Does it mean that outcome of 60% of your games is being decided by just your actual uphill or downhill performance? It even sounds ridiculous. This concept came probably from some Immortal player that has played on low ranks and claimed that there is no Elo Hell.

Reason why you are not climbing is DEFINITELY in some part caused by poor skill of your random teammates. However, in most cases you can't do nothing about it. Remember that you are only capable of managing yourself. Therefore, improve your own skill or get a 5-stack. With time, some luck and correct plan - you should reach your dreamed rank eventually.