from a numbers perspective it is not debatable, who have been the most important this year.
1) Giambi 2) Damon 3) Jeter
Offensive #s is a part of the game, not the only part or the most important part.
From a #s perspective, Ortiz leads in HRs and RBIs, yet he is 5 1/2 games out of first.
It's more than just simply numbers. The Yankee Captain provides leadership and cohesiveness to the team, especially on the field. The spectacular run saving defensive feats of Jeter only shows up as an assist in the box score. Preventing runs is an important part of the game which you seem to neglect.