If I may....
I find arguments predicated on what early Church members (leaders or not) did or didn't due dubious. Logically, the appeal to prior practice (or thought) does not, in and of itself, prove anything, especially since 1) it took the early Church about 400 years to settle and formalize Christian doctrine, and 2) the ECFs often held very diverse points of view, some of which were clearly irrational. For example, early writings often describe hell as being "
eternal," but that is incorrect if hell is a created part of creation. It can be everlasting, but not
eternal. The word "
eternal" means infinite in all directions
(going backwards prior to creation's being created and goring forward after creation is destroyed - if such a thing does ever occur). The op is correct to date the belief hell might be rehabilitative to the third century, but not all rehabilitative viewpoints were about purgatory. Origen (circa 185 - 253), for example, would more accurately be called an
apokatastasist, not an adherent to the doctrine of purgatory. In fact, Origen appears to have held a view much worse than that of purgatory. He was an early universalist. He believed because we all came from the same source, all humans would eventually return to that same source. For the RCC purgatory is a place where only the already saved go. A universalist might make an appeal to Origen and say, "
See! Universalism goes all the way back to the early Church.......
so it is a valid position to believe."
That's just nonsense.
What we
(all Christians, whether Roman or not) should be doing is measuring doctrines by well-rendered scripture and
that is where the problems with purgatory become apparent. Roman Catholicism bases the doctrine of purgatory on apocryphal writings, not scripture. It's also important to have a correct understanding of purgatory because many Protestants confuse purgatory as a means by which people avoid hell but that is not what the RCC teaches. In RCism, purgatory is a place where the
saved go to be purified before entering heaven. People judged and sentenced to hell do not get to go to purgatory. Because nothing impure can enter heaven, those who've died in Christ have various degrees of impurity that need to be cleansed from the person before he or she can enter therein. It's still a wack position, but it's not to be construed as a waystation between heaven
and hell. Everyone in Purgatory is going to heaven and never to hell. As
Catholic Review puts it, "
A person in purgatory is one who is ultimately and surely destined for heaven."
I guess that repentant thief on the cross was pure because he was told he'd be with Jesus in paradise
that day! He must have been wrongly convicted, too

.
Luke 23:39-43
39One of the criminals who were hanged there was hurling abuse at Him, saying, “Are You not the Christ? Save yourself and us!” 40But the other responded, and rebuking him, said, “Do you not even fear God, since you are under the same sentence of condemnation? 41And we indeed are suffering justly, for we are receiving what we deserve for our crimes; but this man has done nothing wrong.” 42And he was saying, “Jesus, remember me when You come into Your kingdom!” 43And He said to him, “Truly I say to you, today you will be with Me in Paradise.”
Oops! Not innocent. Justly convicted and sentenced. Musta been a Special Passover Dispensation, I guess

.
The purgatory doctrine is based on 2 Maccabees, which is a text rejected by Protestants. That alone is a little odd because the EO churches use the apocrypha, but they do not hold to the doctrine of purgatory. Other supporting texts used by the RCC are Matthew 5:25-26 and 1 Corinthians 3:11-15. An objective reading of the latter two texts readily provides proof the RC position is highly inferential and not what the text actually states.
2 Maccabees 12:39-45
On the next day, as had now become necessary, Judas and his men went to take up the bodies of the fallen and to bring them back to lie with their kindred in the sepulchres of their ancestors. Then under the tunic of each one of the dead they found sacred tokens of the idols of Jamnia, which the law forbids the Jews to wear. And it became clear to all that this was the reason these men had fallen. So they all blessed the ways of the Lord, the righteous judge, who reveals the things that are hidden; and they turned to supplication, praying that the sin that had been committed might be wholly blotted out. The noble Judas exhorted the people to keep themselves free from sin, for they had seen with their own eyes what had happened as the result of the sin of those who had fallen. He also took up a collection, man by man, to the amount of two thousand drachmas of silver, and sent it to Jerusalem to provide for a sin offering. In doing this he acted very well and honorably, taking account of the resurrection. For if he were not expecting that those who had fallen would rise again, it would have been superfluous and foolish to pray for the dead. But if he was looking to the splendid reward that is laid up for those who fall asleep in godliness, it was a holy and pious thought. Therefore, he made atonement for the dead, so that they might be delivered from their sin.
So the RCC doctrine is based on a specific episode in which Jews prayed for idolators. The use of this text is also problematic because it teaches idolators are godly and there is another means of atonement other than Jesus. I've often wondered why Judas didn't consider the fallen to have fallen
by God's hand because they were idolatrous and God, therefore, culled them from group. If that's the case the Judas' behavior is all the more suspect. God, after all, has a long history in the OT of purging the ranks of Israel
(and doing so using other idolatrous nations to do so before destroying them, too!). This is just one more example in a substantial list of ways in which the Jews mucked up and that muck up led to bad
Christian doctrine.