Anyone who saw Jesus resurrected who had history with Him wrote about Him. The 27 books of the NT are corroborated independent sources. Jesus appeared after His death to the 12 Apostles, to 500 though some did not believe it (reasonably because they had not seen Jesus before), 'other Apostles', Paul, and James brother of Jesus. These are the writers of the NT or they had transcribers a common practice for those who could not write themselves.Not at all. It would be far better in terms of 'evidence' if it had been corroborated by independent sources, casual witnesses, passersby, Roman soldiers, etc, who had no axe to grind or any connection to the alleged eyewitnesses as reported in the NT, but were astonished enough by the events to make a written report. That would count as better evidence, but still problematic.You actually concede it is first class evidence because you can't improve on it.
Would not the best testimonies be those who spent 3 years with Jesus who really knew Him rather than some passerby or Roman soldier whom it is unclear whether they had seen Jesus before He died? You can establish the Apostles spent 3 years with Jesus, Paul's conversion, James' conversion. But it would be of little value to have axe grinding or non-axe grinding people whom we are unclear ever would have seen Jesus before then. Matthew had no axe to grind, neither did any of the Apostles selected. They came freshly anew. Did James and Jude have an axe to grind? It would seem even better to have axe-grinders whom it would seem not in a million years would give their lives to Christ like Paul who was killing Christians and had a cushy job as a Pharisee.
There was nothing to be gained by being Christian only established martyrdom, pain, suffering and ridicule. We should point out too that this collection of data we have gone over together is better than for anyone else in antiquity by far. So you are looking for some crumbs compared to the 3 years spent with the Apostles who really knew Jesus to identify Him resurrected.