What Haruo said - Surely there must have been SOMEONE called Jesus or Joshua or Isaiah around at the time. I find the assersion that there was no-one of that name around at the time rather unlikely. Perhaps, as you seem to set great store by the burden of proof, you would like to explain why these popular names fell out of use during that period and the regained popularity again after. A miracle perhaps?

OK. Perhaps not. Let's apply Occam's razor to the argument.

1. There was someone with a popular name who gained an element of noteriety at the period. Some time later the church that was being established picked up on this noteriety and decided to use the character as a figurehead for their religion. Using bits of history and bits of legend they start to build a believable story.

Or

2. A very popular name at the time, for some reason, fell out of favour for a year or two. Some time later the church that was being established decided to pick a name that had not been used in that period and make up completely unreleated events. Instead of relying on events that some people had heard about they chose to start from scratch and forge completely unverifiable evidence.

Let me see. Which is the simplest and and most likely. Hmmm...

Cheers

DtG