Von Manstein failed to get into Kursk. He got beat.
I think that the 'undefeated criteria' is a little unfair. Sometimes a general is just handed a losing hand and the best he can do is mitigate a defeat (MacArthur in the Philippines; Lee in the Wilderness, etc.) I don't think Phil Sheridan was ever defeated. He was a good general at the tactical & strategic levels, but one one of the greats, IMHO.
Forgot about Kursk. Scratch Von Manstein. Guderian remains, but he was already forced into retirement.
Yes, the undefeated criterion is unfair in determining the greatest general, or the best sports team coach. But it is a nice clear, crisp criterion nevertheless. Some of the world-changing generals of history, Alexander in particular, comes to mind. Was Cyrus the Great ever defeated? His achievement probably exceeds Alexanders, for Alexander had but one great empire to conquer, thqat build by Cyrus, while Cyrus had many.
As to MacArthur in the Philippines: yes, he was dealt a bad hand. But the American forces were not really PREPARED for the onslaught that was coming either. MacArthur was far too passive. The same thing happened in Korea. MacArthur was SURPRISED by the Chinese counterassault. He had intelligence, but he disregarded it. Perhaps he was playing brinkmanship with the President, and thought that the prospect of a sudden reverse might prompt the use of the atomic bomb, which his plan advocated, but about which he was rebuked. It is difficult to say.
I don't have an axe to grind with MacArthur, but it remains true that the Americans weren't just outnumbered in the Philippines, they were surprised. And they weren't just outnumbered in Korea, they were surprised. I might give him a pass on the Philippines, but what happened in Korea was MacArthur's fault.