It's not binary. I had two games in a row with toxic throwers this morning, and that definitely has an impact, but if you're legitimately in a low rank, it implies you are significantly better than the other 11 people in the match. If that were true, you could easily carry and get two to three picks per life, allowing the other equally matched teammates to clean up team fights.
Proof of this lies in the many high-tier players with multiple grand master accounts. It isn't a coincidence, the cream rises to the top.
Tough to accept for me down in gold/plat sometimes, but it's true.