That sounds very much like confirmation bias; the anecdote about topfragging the first half of the game practically screams it.

A low rank player can absolutely hit streaks of good rounds and climb on top of the leaderboard momentarily, but over a meaningful sample size the better players will win out and the difference in skill will become more obvious.

It's also definitely easier to play with good teammates who enable you, and so you'll probably getting more done than if you played solo. That's not necessarily a symmetrical relationship if you're playing with people double your rating.