The word "many" has various meanings. Notice Acts 17:12 (KJV)
Therefore many of them believed; also of honourable women which were Greeks, and of men, not a few.
Many here obviously does not mean all. Many of them, but not all
In Romans 19, we see a contrast. The first instance of many indicates an indeterminate number that signifies all of mankind. All of mankind was judged to be sinners because of one man's disobedience.
The contrast os the second instance of the word "many" in that verse. The second instance also indicates an indeterminate number, yet does not mean all.
We know this to be truth because of Jesus' own words in which He said the wicked would go away into everlasting punishment. If, as you incorrectly assume that all would be made righteous, all would eventually be removed from a state of punishment, then we must also conclude that the righteous who are given life everlasting will one day come to a place where their life everlasting will also be removed from them and they will die.
But this makes the Lord Jesus Christ a liar, who promised that those who believe in Him that they would never die.
Your position is wrong, it makes Our Lord a liar, and nullifies the need for Christ to have suffered and died on the cross.
If one could spend time in the lake of fire and be cleansed of sin, there was no need for Christ to die.
Your position is blasphemous and heretical, to say the least.