Depending on what era in history, a general has to count on one element of his army in order to achieve victory.
In baseball, that is the starting rotation. So much emphasis and money is put into five arms.
The Cubs are probably going to war with these five starters: Lester, Arrieta, Hammel, Hendricks and T. Wood.
The Cubs rotation, if they match last year's production, would generate 14 WAR.
Lester: 3.6
Arrieta: 5.3
Hammel: 3.1
Hendricks: 2.9
T. Wood: -0.9
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Total: 14.0 WAR
In contrast, the champion Giants starting rotation accumulated 8.1 WAR.
Bumgarten: 4.0
Hudson: 1.5
Vogelsong: 1.2
Peavy: 2.1
Cain: -0.7
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Total: 8.1 WAR
The Giants had several starters with injuries so it cobbled together a 6th, 7th and 8th starter. But it was the timely offense that made up the slack in SF's championship run, with a 22.3 oWAR to a pitching staff total 15.2 WAR. The Giants win percentage above average was .505.
It is debatable what is replacement value for a starting pitcher (a .500 record? or more tied to run production .300?) as a factor of team wins. A GM would like a replacement pitcher to win at least half their starts; but realistically a third is probably a better gauge (since the burden falls more to the bullpen).
Each team has 162 games to start. Each rotation pitcher probably, on average, will take the mound around 31 times. So a set rotation covers about 155 games. A replacement team would average around 65 wins. The Giants patched together an 88 win season, meaning the offense carried at least 15 games above pitcher replacement (almost double value than the starters).
The Cubs won 73 games with batting WAR of 7.7 and pitching WAR of 15.7, almost a mirror image of the Giants. The Cubs primary starting five had a collective 7.2 WAR. Again, if one thinks that the 2015 rotation will be much better (by 7 games), this gets the Cubs projected to an 80 win season if the offense remains the same (which may be the case with the young players and league adjustments).
So the Cubs will really have to rely on their starters to carry the team.
