That’s a possibility, and I don’t doubt that the rinky-dink details such as the semi-divine origin of the rulers, how they took turns sharing power and so forth were all typical of Plato’s thought exercises on politics. The fact remains that the continental shelf was dry land 10s of 1000s of years ago, and repeatedly submerged and exposed a number of times over the past two million years, the period when humans were coming around. IOW, Plato’s literary device was based on very old oral traditions which were, like the secret word in the game of telephone, altered in transmission over hundreds of generations, or perhaps many more generations than that.
That was the exact thought behind my first post on this. Oral traditions (I always think of Bill Clinton when I write that) of catastrophic post-glacial flooding would likely have been passed down to the Greeks. But you don't really have to reach nearly that far back to find catastrophic historic events that very likely gave Plato the Atlantis notion.
In 373 BC, a violent earthquake, accompanied by a tsunami, destroyed Helike and Bura, two cities situated on the southern shores of the Gulf of Corinth roughly 150 km west of Athens. Plato was in his mid 50s at the time. Helike was the capital of the Achaean League and revered throughout the ancient world as the cult centre for worship of Poseidon. (Recall that Plato’s Atlantis was ruled by a powerful and remarkable dynasty of kings arose directly from Poseidon, god of sea and of earthquakes).
This was a period when Greece was victimized by numerous large and deadly earthquakes. Earlier, in 426 B.C. an earthquake-caused tsunami had either destroyed or created the island of Atalante (historical accounts differ). I’m pretty well convinced that Plato’s literary/philosophic conception of “Atlantis” was a fictional cautionary tale based on these historic events and others.
Don’t forget the great Spartan earthquake of 464 B.C. that ushered in the “Earthquake War” between Sparta and Athens. As one writer put it: “At the end of a century that had witnessed one of the most violent earthquake storms to have affected the ancient world, ordinary Greeks probably didn't speculate on the origins of the mythical Atlantis; they were too busy surviving its reality.”