There's a big difference between a Jesus constrained by the laws of physics, and a Jesus who performed miracles. Proving that there was a Jesus constrained by the laws of physics doesn't lend credibility to the Bible. It actually demolishes it. Now which Jesus are the historians talking about? Just a guy named Jesus? Or a miracle Jesus? If it's the first, well, OK, maybe, why not? If it's the miracle Jesus, then that sounds like bullshit. If all you can do is prove there was a guy named Jesus, well whoop-de-doo. You haven't got Jack. And no one has been able to prove that, anyway. I've never understood the point of arguing about the existence of just a regular guy named Jesus. It's a waste of theological discussion and hurts Christianity more than it supports it.
Historians generally lean toward the belief that the Jesus mentioned in the Bible was a real person. To my knowledge no mainstream, respected historian has ever spoken about his time at Hogwarts. You are correct in that proving that a man named Jesus used to be walking around claiming to be the son of God absolutely does not in any way support any of the magical claims of the Bible. But the OP wasn't about the magic powers of Jesus, just whether or not he had existed.
Of course proving a mundane thing does nothing to even remotely suggest that associated fantastical claims have any basis in reality. And of course nobody here thinks it does. Christians only see it that way because all they can do is prove the mundane. It's all they have, so they elevate the significance of anything the Bible got right. Many years ago I heard what was essentially a claim that archaeologists had found Sodom and Gomorrah, which they had previously not believed to have existed, and this proved the Biblical account of the two cities. To understand why mundane evidence is more significant to a theist than it is to a reasonable human being you have to understand how they think and why.
To the theist, getting just ONE THING wrong brings the whole house of cards crashing down on them. Prove the entire planet wasn't flooded, the story of Noah's Ark isn't real and the Bible can't be taken literally. Entire religious sects cease to exist. Prove evolution happened and the Biblical account of creation didn't happen. Again, entire religious sects cease to exist. Prove Jesus wasn't magical then nothing about his life is correct, including him rising from the dead. Pretty much all of Christianity dies that day. Sure, it would be replaced with something just as stupid immediately as people try desperately to hold on to as much of their belief systems as possible, but its current for dies overnight. This is, of course, ignoring the fact that Christians are adept at ignoring facts so what you "proved" would, like the Bible, be "open to interpretation".
That is the mindset Christians come from. Prove ONE SINGLE THING wrong and their entire belief system gets tossed out. So that is how they see the world. Archaeologists are "scientists". Scientists are a group of evil "smart people" with a hive mind who are desperate to do nothing more so than to kill God. So if archaeologists say "This probably never existed" and then they're proved wrong they get to toss out ALL of science that they disagree with. And, of course, all scientists have that hive mind thing going on, so they all say exactly the same thing (when it's convenient, of course. As Randy showed us, when it's not convenient you get to choose the one who agrees with you and throw out the thousands who don't). So if you can prove ONE SINGLE SCIENTIST wrong then you have proved EVERYTHING you disagree with wrong. Thus, prove that Jesus really walked the Earth, something all scientists everywhere dispute, and you have proved the Bible in its entirety.
We all know that's stupid. We all get physically ill over the flawed logic of that way of thinking. This wasn't one of "those conversations", though, so all the bullshit logical flaws can (thankfully) simply be ignored in this context.