>>Could you please tell me what heinous crime merited being crucified on a tree, yet minutes before His own death our LORD told the man “Assuredly I say to you, today you will be with Me in Paradise”? Because it doesn’t sound like the dude hung out in this alleged Purgatory for very long.<<
He was the thief on the cross. Sheol, prior to Jesus death and resurrection, had two levels. The lower level for people who were not saved, the second level for those who were. Jesus had not paid the price yet so those saved could not yet go to heaven. After Jesus died on the Cross He went to the second level of Sheol and released those souls and took them with him to heaven. The unsaved souls in the lower level are still there and will be sent to Hades with Satan.
IOW, "The gates of Hades shall not prevail against it"
Nobody is there anymore.