I think it is much more that he rejects the Church understanding of the Gospel as being wrong, as it did not accept that to him Judaism was still able to save in time of Jesus and paul!I agree, as he starts out "I am not an expert on the subject". This is why many reject Wright, and probably the difference in how they reject him compared to how those who are experts reject him.
The author assumes 2000 years of viewing a certain way. In truth, we only know of 500 years. Also, Wright himself has stated his NPP is probably not right, that we need to move from the Reformation and to Scripture. The problem people have is not the NPP but the NPP's rejection of a 16th centurey Reformation/Catholic view of Paul and the Jewish religion.
This is, I believe, what Wright is addressing in the article - 5 centuries of tradition vs Scripture, with Reformed theology taking place of the RCC.
So per him, if someone did not have real background in Judaism of that time, the Gospel and Pauline Justification could not be proved/taught by the Holy Spirit from scriptures themselves?