I think what you're saying is, just because there's no evidence doesn't mean something did not happen. That's true. But the possible unreliability of contemporary accounts doesn't apply to a situation where there are no contemporary accounts.
In a situation where the only accounts are of undetermined origin, where the original accounts have not been found, where the only copies are literally that- hand-copied accounts that come with the caveats of such a process... it is natural to express doubts, even if those accounts reported normal or mundane happenings.
If these accounts also report on supernatural events, possibly involving actual deities, our skepticism must be ratcheted up. Otherwise, we are left with many, many such claims from people throughout the past that are suddenly possible.
I'm not sure that the gospels would fare as well as, say, Joseph Smith's accounts, if we decided to create a "minimal facts approach" for the latter.