What does any of that have to do with what I wrote. The real question is this - Was Brady's QB rating the lowest since 2003 because he isn't as good as he once was or was it because of his supporting cast? I think Brady is still a great QB DESPITE the subpar (for him) QB rating. IMO, it's not really worth debating. The QB rating is affected by the rest of the team's performance. If that is true for a great QB like Brady, then surely it can be true for Tannehill.
QB ratings fluctuate by a significant amount during their careers. Brady's jumped by 30 points in one season from 2006 to 2007. Did he magically become a much better QB in one season? No, the receiving corp went from Reche Caldwell and an old Troy Brown to Randy Moss and Wes Welker. Likewise, his rating dropped by more than 10 points from 2012 to 2013. His receiving corp went from Welker, Brandon Lloyd, Gronk, and Hernandez to Danny Amendola, Julian Edelman, and 4 fewer games with Gronk.
I don't know how to make it any clearer. QB rating is a whole team stat. Heavily influenced by the QB but still a whole team stat.