Purgatory is, indeed, a curious concept. In traditional Catholicism the only difference between it and hell was the duration, the former being eternal and the latter of some unknown quantity of time. Today, however, Purgatory is widely marketed in the Catholic Church as being a relatively pleasant experience, akin to taking a refreshing shower before entering the gates of heaven. It seems peculiar to me that individuals would actively seek indulgences to reduce one's sentence in Purgatory, yet many Catholics have spent enormous fortunes and exerted massive effort for that very end.
For example, your claim that there is no difference between hell and Purgatory exception duration. False. The catechism says that "The Church gives the name
Purgatory to this final purification of the elect, which is entirely different from the punishment of the damned"
People tend to forget that "fire" images abound in Scripture that have nothing to do with hell but everything to do with refinement and purification and images of God.
God manifested in the burning bush (Exodus Chapter 3)
God descending on Mt. Sinai as fire (Exodus Chapter 19)
God as a pillar of fire leading the Israelites across the desert (Exodus Chapter 13)
Elijah taken to heaven in a chariot of fire (2 Kings Chapter 2)
Tongues of fire at Pentecost (Acts Chapter 2)
Hebrews 12:29 says “for our God is a consuming fire”
Revelation 1:14 say of Christ that “his eyes were like a flame of fire”
And then St. Paul's description of the burning away of the wood, hay, stubble in our lives on the day of judgment:
1 Corinthians 3:11-15 11 For no other foundation can any one lay than that which is laid, which is Jesus Christ. 12 Now if any one builds on the foundation with gold, silver, precious stones, wood, hay, stubble— 13 each man’s work will become manifest; for the Day will disclose it, because it will be revealed with fire, and the fire will test what sort of work each one has done. 14 If the work which any man has built on the foundation survives, he will receive a reward. 15 If any man’s work is burned up, he will suffer loss, though he himself will be saved, but only as through fire.