‘In the absence of evidence to determine which religion is actually right, how can you reconcile all these divergent beliefs with science?’
Your question also relates to science. In ‘The Structure of Scientific Revolutions’, Thomas Kuhn gives several examples showing that progress in science is not as objective as many would let on. Max Planck said, ‘A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.’ So, scientific ‘evidence’ can lead to divergent beliefs in science. Beliefs that are held due to personal preference.
But to answer your question: ‘Why should Christianity be the truth?’
Because the other systems are constructions by men - systems that fit within man’s reasoning. Christianity is God’s revelation to man - God declares who His is, who man is, etc. Jesus is central since His is God’s revelation in flesh.
Men don’t want to have to answer to God, so they made up ‘religions’ to justify themselves. They believe that if they hold up their part of the contract (the one they wrote out according to their own understanding) then God is obligated to honor their efforts. So, they make themselves equal to God.
You see, Christianity is not about knowing or discovering facts like science. It is about attitudes and motives in relation to God and other men first. In Christianity God reaches down to transform men because men cannot change themselves in their own power.
Science cannot make us moral beings because morality is not based in the mind but in the soul. Honest scientists do not honor honesty because honesty was discovered or proven by science. They honor honesty because they are moral beings first.