If Jesus did not die a violent and imminent death, then that makes him a false prophet. But the Qur'an says that he's a great prophet, and so the Qur'an would be wrong and thus discredited. On the other hand, if Jesus did die a violent and imminent death as he predicted, then he is indeed a great prophet-but this would contradict the Qur'an, which says he didn't die on the cross. So either way, the Qur'an is discredited.

No credible historian worth his salt would ever place the Qur'an as a more credible source on Jesus over the New Testament.