Christianity is a belief in Christ, not a maths problem. Take off your
scientism glasses when looking at religion.
Christians are all unique individuals, with different backgrounds, strengths, weaknesses etc. That will affect how we view God and religion overall. We all come from different stages in our life and have a different life map but are walking towards the same destination i.e. God. Someone walking from the east will see the same mountain very differently to someone walking from the west.
No, both can be right AND both can be wrong. The truth will stay the same regardless of what any christian says. The truth never changes. Two christians can read the same bible verse, see something completely different and be right.
There is therefore now no condemnation for those who are in Christ Jesus. (Romans 8:1)
Jack sees
There is therefore now no condemnation for those who are in Christ Jesus. (Romans 8:1) Jack rejoices that because he has faith he is no longer condemned because he now knows God has forgiven him.
Jill sees There is therefore now no condemnation
for those who are in Christ Jesus. (Romans 8:1) Jill now realises that belief in Christ is what is absolutely essential to be accepted by God. People who are not christians are condemned by God.
One bible verse, two different perspectives, both completely correct.
The God of the Old Testament is the same as the God of the New Testament. Yes there are many christians who try to explain away how much sinful people were punished by God before Jesus came. Their rationalising and excuse-making does not change the truth.
Have you ever read anything about what the Jews had actually been doing when worshipping pagan gods before they were punished by God (after many warnings by different prophets)?!!! It sounds like you need to learn about ancient religions' terrible customs and sacrifices before you can point the accusatory finger at the Christian God.