A Jewish Rabbi existing and being later transformed by storytelling into Jesus is as good as Jesus never existing if the Jewish Rabbi bears no resemblance to Jesus in any way, which is likely the case given how little of a mark this Rabbi must have made on his higher profile contemporaries (none of them ever mentioned him). All knowledge about Jesus comes from writings that originate years after his supposed death. So whether it's likely or not, his existence remains a hypothesis and must be treated as unknown till proven true.
The fact that the existence of Nazereth in the 1st century as anything more than a city of the dead remains in dispute still means that the onus is on believers to demonstrate that it existed. As yet it remains at best unproven.