I have some disagreements from your post.
First, the word "dispensation" has been used in non biblical writings since the Apostolic Fathers. How does the use of this word prove dispensation theology? Submitting as evidence the use of this word for proof is a word fallacy, in my opinion.
The word "dispensation" is biblical. That's why it was used by the Apostolic Fathers. Even John Calvin used this word and he sure wasn't a dispensational! If dispensationalists limited the word "dispensation" to its biblical use only, we would not be having this discussion. But the word since the mid 1800's has been "hollowed out" and given a non inspired, theological meaning. The hard nose distinction between redeemed Israel and the church which Darby introduced has no relation to the biblical use of the word "dispensation".
Secondly, you submitted a quote by Irenaeus which has been discussed in Christianforums.com before, and found seriously lacking in support of a pre-tribulation rapture. So why bring it up again? Is this desperation to prove a theology that was non existent before Darby's generation (I say this respectfully)?
You quoted: "And therefore, when in the end the Church shall be suddenly caught up from this, it is said, 'There shall be tribulation such as has not been since the beginning, neither shall be." ---end of your quote---
Now to the rest of the story....
Problem #1: the last sentence quoted (from Irenaeus) is referring to a passage in Matthew during the tribulation: "For then there will be great tribulation, such as has not been from the beginning of the world until now, no, and never will be." (24:21). So what was the church doing in the tribulation? Anyone who reads the timeline in Matthew 24 up to this verse and is objective should be able to spot this problem, unless their dispensational presupposition drives the text.
There are further problems with your quote. You may have intentionally left off the next sentence by Irenaeus: "For this is the last contest of the righteous, in which, when they overcome, they are crowned with incorruption". This "last contest" is contextually linked to the word "overcome" which is further evidence the church was in the tribulation. See book of Revelation. But there are more problems.
When the underlying Latin text is examined that was used for our English translation of Irenaeus's writing, it doesn't appear to support the English translation of: "when in the end the Church shall be suddenly caught up from this". According to this page:
http://www.fivedoves.com/letters/july2014/marilyna76-2.htm a more accurate translation from Latin is the following: "And therefore, when the end is suddenly here, the Church will be taken away."
Finally, on a previous thread, another English quote is provided by Irenaeus that has the church in the tribulation:
"In a still clearer light has John, in the Apocalypse, indicated to the Lord's disciples what shall happen in the last times, and concerning the ten kings who shall then arise, among whom the empire which now rules [the earth] shall be partitioned. He teaches us what the ten horns shall be which were seen by Daniel, telling us that thus it had been said to him: "And the ten horns which thou sawest are ten kings, who have received no kingdom as yet, but shall receive power as if kings one hour with the beast. These have one mind, and give their strength and power to the beast. These shall make war with the Lamb, and the Lamb shall overcome them, because He is the Lord of lords and the King of kings." It is manifest, therefore, that of these [potentates], he who is to come shall slay three, and subject the remainder to his power, and that he shall be himself the eighth among them. And they shall lay Babylon waste, and burn her with fire, and shall give their kingdom to the beast, and put the Church to flight. After that they shall be destroyed by the coming of our Lord." ---end of quote---
For further information about the quote from Irenaeus above, please see:
http://www.christianforums.com/thre...id-and-post-trib-are-all-wrong.7625498/page-2 (see post #37).
I find no evidence from the Apostolic Fathers that the early church believed in a pre-tribulation rapture and a hard nose distinction between redeemed Israel and the church that traditional dispensationalists hold. This alone does not determine one's salvation. While this topic is important, I don't believe it is a core doctrine of the faith that should divide us.
Above all else, keep the faith in Jesus Christ.
In Christ!