And the so-called "sophisticated modern theologies" define God so vaguely you can't reach any conclusions about what he's like, or what he would and wouldn't do, or how a world with him in it would be any different than a world without him. They define God so abstractly that he might as well not exist. (Either that, or they actually do define God as having specific effects on the world, such as interventions in the process of evolution -- effects that we have no reason whatsoever to think are real, and every reason to think are bunk.)
So to persuade us -- me, anyway, and I suspect many other atheists -- that a religion was correct, it would have to do more than show evidence of a few miracles in our time. It would have to explain why those miracles were happening now... and yet had somehow never happened before. It would have to explain why the world had always been best explained by physical cause and effect, but now, overnight, that had changed. Even if a 900-foot Jesus appeared in the sky tomorrow, healing amputees and unambiguously stating his message in all languages and whatnot, a religion would have to explain why God was making all this happen now...and not at any other time in human history.
The fact that religion has utterly failed to do this in thousands of years doesn't mean that it never, ever could. I could imagine, for instance, a malevolent trickster god, who's deliberately hidden all traces of his existence from us for hundreds of thousands of years...but who today, just to screw with us, has decided to show his existence by healing amputees, moving Earth into Pluto's orbit without anyone getting chilly, writing his name in the sky in letters 100 feet tall in every language known to humanity, and making all members of the Wisconsin Evangelical Lutheran Synod, alone among all other religions, healthy, wealthy and successful beyond anyone's wildest dreams.
I don't want to get into that particular argument (the idea of advanced space aliens that have "godlike" powers) right here. What I do want to point out is that my conclusion -- my acceptance of the trickster god hypothesis in the face of healed amputees and changed orbits and Loki's name in the sky and so on -- would be provisional. It wouldn't be a fundamental axiom or a tenet of unshakable faith. It would be a provisional conclusion, based on my best understanding of the best currently available evidence. If I concluded that the trickster god hypothesis was the best explanation of these weird phenomena, and then someone showed me convincing evidence that it was really super-advanced alien technology...I'd change my mind. I would renounce Loki. It'd be a provisional conclusion; a falsifiable hypothesis.