I think head coach is somewhat of a proxy for the quality of the assets surrounding the QB and tend to consider QB / Coach combo in the greatness concept. Montana/Walsh,Young/Walsh, Brady/Bellichek, Mahomes/Reid, Kelly/Levy, Elway/Shanahan
Peyton Manning and Ben Rothelisberger both won multiple super bowls with different head coaches, so clearly QBs can transcend coaching limitations.
In recent decades the QB most limited by his supporting cast may have been Aaron Rodgers. In his peak years his play was as good as anyone who ever played the position