Thanks to Midget-Sasquatch, Knohl's earlier article is available from the parallel thread: http://www.jehovahs-witness.com/10/161628/1.ashx
It's definitely worth reading.
He says further that such a suffering messiah is very different from the traditional Jewish image of the messiah as a triumphal, powerful descendant of King David. “This should shake our basic view of Christianity,” he said as he sat in his office of the Shalom Hartman Institute in Jerusalem where he is a senior fellow in addition to being the Yehezkel Kaufman Professor of Biblical Studies at Hebrew University. “Resurrection after three days becomes a motif developed before Jesus, which runs contrary to nearly all scholarship. What happens in the New Testament was adopted by Jesus and his followers based on an earlier messiah story.”
This is anti-Christian Jewish propaganda. There have always been two messiahs. One through the line of Judah and one through the line of Joseph. The "suffering messiah" is the one through the line of Joseph.
There is no threat to Christian faith as long as you separate the messianc references when necessary for either the first or second coming.
For instance, the suffering messiah is the messiah of the second coming and is a sinful, imperfect person. This is the same imperfect messiah of Zech 3 where you have the messiah appearing with befouled garments representing his past life of sinfulness though now he is repentant.
This messiah is not the same as the first-coming since this is an honorable messiah of noble birth, obviously a stand out teacher and rabbi and a man of great glory. He's no "suffering messiah" in general just as you note. But there is no conflict in scripture.
Basically the first coming is about the SACRIFICE and the perfect messiah. The second time is as king-priest like Melchizedek. The first time Jesus arrives he is in a perfect body. But the second time he uses the body of the imperfect prodigal son, which is the only way the glorious, perfect Jesus in heaven ends up with a sinful past. It's not really his past, only the past of the body/identity he becomes at the second coming.
The parables of the Rich Man and Lazarus as well as the prodigal son reference the "suffering messiah" of Isa 53. Jews often point out, as you have above, that the messiah of the 1st century was strong and glorious, hardly a "suffering" imperfect man. But they don't often acknowledge two messiahs and a first and second coming, but like to use Isa 53 to dismiss the fulfillment by Jesus of the 1st century.