The Christian religion must have had a founder. And if the religion claims it's founder was Jesus, then it is logical to assume someone by that name actually existed in order to gather the original followers of this religion.

It's not that great of a steel man as you think. If I'm as bad faith as you and view everything through an extremely skeptical lens, I'd say Christianity could have been started by a rouge group of pharisees who spread the rumors about Christ and His teachings. There's even motivation for that. Have you red 1984? Remember when it was revealed to Winston that the whole liberation movement and its leader was a psy op made up by the party? The Wizard of Oz is another good analogy.

The best argument is a transcendental logical argument and I served it to you. If you are skeptical about Christ's historicity and you apply the same standard, you have no reason to believe most of what you assume to know about ancient and medieval history because much of it was not written at the time of the events by people who witnessed them - rather it was a retelling of events based on testimony or sources that were eventually lost (what most likely happened win Tacitus' case).