It is called a dichotomy. Either the thief on the cross was going to be with Jesus in paradise that day, or not. One or the other. Luke 23:43 And Jesus said unto him, Verily I say unto thee, Today shalt thou be with me in paradise.
If the catholic teaching is true, then the thief would not be in paradise "today". Rather, the thief would have to go to some other place to be "perfected". You can't have it both ways.
If you move the comma you could question when the man might be with Him in paradise. “Verily I say unto thee today,thou shalt be with me in paradise” (someday). He probably didn’t have the heart or the time to tell the poor thief about purgatory!!!