The Giants are not as good as the Saints or Packers. They’re probably not as good as the class of the AFC either (Ravens, Pats etc..).
That does not change the fact that when you absolutely have to have a game winning touchdown drive, Eli Manning plays great and has authored a large number of them including - and I’m not overstating it here - the single greatest play in the history of the Superbowl.
He’s proven himself to be a clutch player.
It also helps when you're going up against the Cowboys' defense.