I think Lemmy has a problem with history in general, since most people on here have degrees/training in STEM. I see a lot of inaccurate “pop history” shared on here, and a lack of understanding of historiography/how historians analyze primary sources.
The rejection of Jesus’s historicity seems to be accepting C S Lewis’s argument - that if he existed, he was a “lunatic, liar, or lord,” instead of realizing that there was nothing unusual about a messianic Jewish troublemaker in Judea during the early Roman Empire.
His name in Aramaic, which was what he almost certainly would have actually spoken, was almost certainly Yehoshuah, which was a common name at the time.
It was often shortened to Yeshua, sometimes to Yeshu.
(This is still a common surname in Hebrew to this day.)
When translated into Greek, this became IESUS.
This is because Greek doesn’t really have a representation of Y as consonant, and because Greek also doesn’t really do the ‘sh’ sound, that got changed to just an ‘s’.
The earliest Gospels that we have are largely (entirely?) written in Greek, because:
Most people of the time were illiterate or functionally illiterate, and most people who learned how to write, well they were taught Greek, because it was the most common shared language of business and governance in the eastern Mediterranean.
There was very obviously a push to proselytize to Greek speakers, the Gentiles, to grow the movement outside of Judea, by many early Christians.
Anyway, yeah, you are correct that the harder J consonant did not develop until much, much later, in Europe.
So… if you were to do a more modern, direct translation of Yehoshuah, to a modern name in modern English, it would roughly be Joshua / Josh, not Jesus.