Well one question is what people mean when they say, “exists”.
Does Santa Claus exist, for example? Most people would say, “no”, even though the St. Nicholas was actually a person and saint. Clearly the popular presentation of him as a still living being, living at the North Pole is fantastical. But it is a wild distortion of a historical figure, not 100% made up from whole cloth.
Back when Diogenes the Cynic was on the site, we argued about this with Moses. His position (as I understood it) was that there’s so much fantasy in the story that it’s not useful to call Moses real. I’m, personally, more ambivalent on that. I accept that, if there was some event that inspired Exodus, it’s probably so far removed from the tale we’ve been told that it really tells us nothing about whatever person was at the middle of the adventure. He might not be named anything like Moses (the name Santa Claus is completely unrelated to St. Nick, for example), he might not have been in Egypt, he might not have been a slave, he might not have been fleeing anyone, he might have been a she, or a couple… Personally, I’m willing to accept that, despite all that, there could be something and someone who are the progenitors and minus any better term it’s most useful to call that event the Exodus and that person Moses, until we have better information on what names to use, and I’m willing to say that there’s a 10% chance that there was some historical event or person that inspired all this.
But I can easily see how using these terms and taking about the original events and people could confuse people, when we’re accepting that the real story might share almost literally nothing with the stories in the Bible. And for the purpose of saving confusion, it’s more useful to say that it’s false and, minus evidence to the contrary, just a fiction. Why presume a factual basis when also presuming that the factual basis shares nothing with the reality?
So it does need to be made very clear that by saying I think David most likely existed, I don’t mean that he existed as written. Most or all of it may be fiction. His name might not have been David. But I do think that there is a person who inspired the story, and in this case I think that the bare bones, between the lines version seems plausible enough that it’s worth treating like it had historic merit. The Goliath story, in the other hand, thpppt.