The whole idea of Atlantis existing....comes down to the way that Plato was told the story in his youth....by his grandfather.
The grandfather? He'd sat in the presence of Solon, a older Greek guy who'd become a statesman in his older years. In his youth, Solon had been a traveler, and gone off to Egypt where he wandered into a temple.....getting a 'speech' by a Egyptian temple-boss....who spoke of Atlantis of the past (9,000 years ago).
So you are relying upon a story....told by three guys, over the space of fifty-plus years, an Plato remember all of the story in the context that each told the story, and putting this to paper.
This is my chief problem in the Atlantis story. Beyond Solon, there just isn't any mention anywhere of Atlantis.
Fictional? Partly true? Mostly true? Anyone's guess.
The Egyptian-temple-guy telling a mostly true story, but Solon making up fifty-percent to add to the story? Well....you just can't be sure of this.
My belief is that I'd like for the story to be entirely true....but having to rely upon three guys to tell the same story....is a pain.