Although I agree that Yeshua of Nazareth was a real historical figure, your argument is fatally flawed.
What other institution? Islam is but 500 years younger than Christianity, while Buddhism is 400 years older. The earliest Hindu Vedas date to at least 1,100 BC. Judaism goes back maybe 4,000 years. And that's just religions. Other institutions lasting that long? City-scale government has been around for 5,000 years. Agriculture is about 11,000 years old. But then, those are practical applications, so I guess it's unfair to compare them to religion.
But all this is ignoring the fundamental problem here: lots of people believing in something doesn't make it true. Lots of people used to believe the world was flat; and moreover, many people still don't realize that this theory was debunked in the 4th century BC by the Greeks, rather than by Columbus, who in fact merely believed the world was a smaller sphere than was believed at the time (he was dead wrong and would have died if a hitherto-unknown continent hadn't happened to be in his way).