crashman wrote:Sima Yi wasn't involved with Cao Cao in his Heyday.
The poll asks who did the most for Wei, not for Cao Cao specifically. While Sima Yi may not have come into his own until Cao Cao kicked the bucket, I still think he did a lot of nice work for Wei.
Cao Cao recognized his talent early on, even when he didn't fully utilize him.
Sima Yi was instrumental in holding Zhuge Liang out of Wei. What would have happened if Yi hadn't been there?
In addition, when Wei was in danger of falling into decadence under Cao Shuang, Sima Yi made the decision to take him out and restabilize the place. I know that Wei fell to pieces shortly after this, but that was after Sima Yi had gone to a better place.
While I certainly agree that the others on this list, specifically Xun Yu and Guo Jia, were very important in the establishment of Wei, I think their successes were comparatively limited to a short period in the kingdom's development.
PS: I guess it's odd for me to go with Sima, since my area of study is mainly pre-220 Three Kingdoms period (technically Later Later Han I guess), but I still give him credit.