I agree. Plato started as a genuine disciple of Socrates and used his early dialogues to promote Socrates' approach to philosophy. However, later. as Plato developed more of his own ideas, he used the dramatised version of Socrates as a sock puppet.
That aside, just because Plato mentioned Atlantis, it doesn't mean either that it existed, or that it was based on some historical place or event.
I can see a similarity between people searching for the "real" Atlantis, and people who believe in, or even "worship", Slender Man. In each case, a fictional creation has caught the imagination and has come to be treated as if it "must be in some sense true."
Pratchett describes the geography and physics of the Discworld in far more detail than Plato described Atlantis. Will we one day have a fringe movement of astronomers proposing competing theories about the "real historical" origin of the Discworld?