If you have done your research, most people were reliant on oral tradition. In fact, some didn't even know how to read or write. The texts we see from that time period were written by the upper class. Did Jesus preach to the upper class? Yes. What did the upper class think? We don't have time for this kind of guy or we need to get rid of this guy he is causing me to lose power or whatsoever. This is why Jesus preached to the lower and middle classes. Luke 14: 16-23 proves my point,
"16 Jesus replied: “A certain man was preparing a great banquet and invited many guests. 17 At the time of the banquet he sent his servant to tell those who had been invited, ‘Come, for everything is now ready.’
18 “But they all alike began to make excuses. The first said, ‘I have just bought a field, and I must go and see it. Please excuse me.’
19 “Another said, ‘I have just bought five yoke of oxen, and I’m on my way to try them out. Please excuse me.’
20 “Still another said, ‘I just got married, so I can’t come.’
21 “The servant came back and reported this to his master. Then the owner of the house became angry and ordered his servant, ‘Go out quickly into the streets and alleys of the town and bring in the poor, the crippled, the blind and the lame.’
22 “‘Sir,’ the servant said, ‘what you ordered has been done, but there is still room.’
23 “Then the master told his servant, ‘Go out to the roads and country lanes and compel them to come in, so that my house will be full. "
This would explain why, in your words, God "transmit[ted] his message in the absolute worst way possible, where nobody can agree how to interpret it."
You also claimed, "both the Old Testament and the New Testament being subject to countless mistranslations and revisions over time". The reason for the countless translations is not because Christians changed the text, it was either to adapt to the language or make it easier to understand/ easier for a certain audience to understand. This makes your claim false.
In addition, God wants people to come to believe based on their faith. He wants it to be an emotional process. If there was tons of evidence then everyone would believe based on the facts and not because they had a revelation in their hearts that Jesus is indeed real. If he had allowed evidence to leak out, he would not have as strong of a relationship with his followers. This would also take out the faith portion of Christianity.