On the one hand, the quarterback is definitely the "first among equals" on a football team. He takes the snaps, hands the ball off, throws the passes and so on. He helps initiate the offense and to a degree, direct where it will go. If he throws the ball to the wrong place, the pass is incomplete or worse, intercepted. If he blows the handoff, the running back will not be able to get up to speed in time to try to move out of the backfield and gain yards.
But on the other hand, the success or failure of a play also depends on hundreds of other factors. Someone's always on the other end of a thrown pass or handoff, and how they perform also affects whether or not the play works. Len Dawson was the most successful quarterback my chosen NFL team, the Kansas City Chiefs, ever had, but a Super Bowl IV without rookie Ed Podolak in the backfield with him or Otis Taylor to throw to or one-eyed Fred Arbanas at tight end leaves him a footnote in Kansas City as well as outside of it.
Move one step along in the process, and the success of a play depends on whether or not a running back evades defenders or keeps his feet, or whether or not a receiver maintains control of the ball when he comes down and stays inbounds. Widen the focus, and a successful play can be erased because an offensive lineman on the other side of the field drew a penalty or a receiver pushed off at the wrong time.
Heck, there's two entire sets of players who are on the field when the quarterback is on the sidelines reviewing game strategy or resting; special teams and defense. To go back to my 1969 Chiefs, Dawson, Podolak, Taylor and Arbanas could be great but without Willie Lanier and Buck Buchanan knocking opposing players to the ground when necessary, their efforts would be for naught. To say nothing of the automatic foot of the great Jan Stenerud, kicking field goals and extra points.
Football is probably the most team-dependent of the major televised sports. A great individual basketball player needs help -- the Chicago Bulls did not begin to dominate until Michael Jordan was joined by Scottie Pippen. Hockey operates similarly. And great baseball pitchers can't do the whole job by themselves either; even Satchel Paige needed a catcher.
I've kind of always thought that giving a quarterback the same kind of won-loss record a pitcher might have is no way to really measure their value, even when it comes to playoff records. Like the column writer says, it's possible to say that because his Indianapolis Colts have lost more playoff games than they've won with Peyton Manning calling the signals, Manning is somehow less of a success as a quarterback. But that kind of evaluation ignores the role Manning may have played in bringing the Colts to those playoff games. So judging his quality as a quarterback probably needs more evaluation than just his team's won-loss record in playoff games in which he plays.
Either way, he's a lot better at it than I would be.