Irenaeus is not infallibly inspired. Neither are his interpreters. I wouldn't want to be handing my anti-theology on the writings of men.
No one said Irenaeus was infallible but he is the closest resource with direct knowledge as to the timing of the writing of Revelation. To directly contradict someone who studied under the person who was a direct Apostle of John is foolish. His statement is the most authoritative we have as to the time. His statement of when Revelation was written and his statement of not knowing the name of the Anti Christ puts Preterists in the category of error.