Christians from both sides of the continuation of spiritual gifts debate understand Irenaeus's quote here more charitably than Gibbon, and do not see it as evidence that people were being raised from the dead in the late 2nd century. I'll refer to the writings of cessationist B. B. Warfield and charismatic Ronald A. N. Kydd.
Warfield addresses Gibbon directly and agrees with his assessment of the period, saying "Irenaeus alone of all the writers of this period speaks of raisings of the dead at all." Eusebius mentions one raising told by Papias from the apostolic age, but his overall work indicates the scarcity of such events:
It is very clear that Eusebius was not familiar with raisings from the dead in his own day, and also that Papias was not familiar with them in his day; and it is equally clear that Eusebius did not know of numerous instances of such a transaction having been recorded as occurring in the course of the early history of the church, which history he was in the act of transcribing. (14)
Warfield cites the writings of several other early authors, such as Theophilus of Antioch and Tertullian. The latter in particular, in On Modesty, XXI, contrasts the spiritual powers of the apostles from their successors, saying that the former "raised the dead." Warfield concludes:
It is an understatement to say that Irenaeus's contemporaries were unaware that the dead were being raised in their day. What they say amounts to testimony that they were not being raised. (14)
So why, then, does Irenaeus say this? Kydd defends Irenaeus as a scholar, citing the vindication of his writings on Gnosticism following the discovery of the Gnostic Nag Hammadi documents in the 1940s. And based on their analysis of the passage, Kydd and Warfield hold that Irenaeus is actually refering to the apostolic-era raisings of the dead, not ones happening in his own day. Warfield writes:
Irenaeus throws the raisings from the dead well into the past. This is made evident not only from the past tenses employed, which are markedly contrasted with the present tenses used in the rest of the passage, but also from the statement that those who were thus raised had lived after their resuscitation a considerable number of years, which shows that recent resuscitations are not in view. (242)
Warfield also notes the phrase, "as we said," which he argues points back to Irenaeus's mention of raisings from the dead in the apostolic era (5.7.2), not recent instances. Kydd summarizes:
Warfield concludes by saying that "there is no reason why the cases he [Irenaeus] has in mind may not have occurred during the lifetime of the Apostles or of Apostolic men," and I think he is right. (45)
- Eusebius, Church History, from Nicene and Post-Nicene Fathers, Series II, Volume 1
- Kydd, Charismatic Gifts in the Early Church, 43–45
- Warfield, Counterfeit Miracles, "The Cessation of the Charismata," 11–16, 241ff.