Thanks, that is the classical argument for the view that Revelations was written in 95AD.
I have already described it as "flimsy at best", so now I feel compelled to explain myself.
It seems to me that the backbone of the argument hangs on the Irenaeus quote that you gave us a translation of.
This translation of course reflects the understanding of Eusebius, who passed it on to us in his commentary on Irenaeus.
The critical line in the quote as you have written it here is:
"for it (the Apocalypse evidently) was seen no very long time ago;"
The reason this translation is disputed is that there is a single Greek word for "it was seen" that can be grammatically translated into "he/she or it was seen".
In the context it may mean that "he" John was seen or "it" the book of Revelations was seen.
You may think I am biased by the historical interpretation I already have of the book, but in reading the entire quote it seems to me that Irenaeus' thoughts make more rational sense if he was referring to John.
if we were to approach the matter not through the church Fathers, but through familiarity with the book and a basic understanding of the major events of the time, including the kings, kingdoms and high priests, what would we conclude about the beast that comes out of the sea, the beast that comes out of the land and the Mother of Harlots?
This is a settled issue, the internal evidence alone is sufficient,
However, the architects of dispensationalism knew this, that is why they had to appeal to outside sources to bolster their claim.