The long and short of it is that Schliemann and Calvert first found a site and then were able to use that site to verify that the Homeric descriptions were accurate. (Later, sadly, it would turn out that Schliemann identified the wrong occupation layer as the probable Homeric Troy.)
So, myths and legends did nothing to find the site; instead, the site’s discovery came before the effort to match a myth to it. Schliemann’s later excavations at Mycenae turned up Mycenaean ruins (which were previously known—he didn’t “discover” them from directions in the Iliad either), but his actual attempt to use Homer’s Odyssey to find a site on the island of Ithaca mentioned in the text ended in failure.
Second, Troy had a continuity in history that fictional locations like Atlantis do not. Troy was occupied from 3000 BCE down to Homeric times, and the ancients had no doubt about its existence because it was still in existence. The site ceased to be occupied sometime after Homer likely composed, probably around 700 BCE. The Romans later built a new city atop the abandoned ruins, Troy having ceded its ancient name, Ilion, to the nearby Roman city of New Ilium. The claim that Troy was nothing but a myth was actually a modern invention, one generated by early modern critical history when early modern scholars were not able to find a physical site to pin to Homer’s poems, which were increasingly seen as fictional rather than historical. But the fact that the Trojan War had no historical support should not have translated into doubts about Troy’s physical existence since every other pre-Classical Greek epic was tied to a specific, and known, city, such as Corinth, Athens, Mycenae, Thebes, and Tiryns (said to be built by Cyclopes!). (So far as I know, fictional places, like Atlantis, Panchaea, and others begin to appear in literature—though not epic—only during the Classical period, several centuries later.)
Today, thanks largely to Martin Nilsson, we know that the ancient Greeks consistently associated mythic tales—fictional though they be—with actual geographic locations from the Mycenaean past, creating elaborate and interlocking (if fictional) histories for these cities. Atlantis fails this test because it plays no role in any mythic cycle and is never mentioned outside Plato and those dependent upon his text. Bronze Age cities were celebrated in epic poetry; Troy was one of these cities, but Atlantis was not.
Now, against this is the fact that a Scot, Charles Maclaren, actually did deduce the location of Troy in 1822, largely from the Homeric description. He even picked out the exact hill, called Hissarlik, where Calvert and Schliemann later excavated.
But he could do this only because Troy, like Athens, Mycenae, Pergamum, and other ancient sites, was and had always been real. It was only early modern scholars who had invented the fable that Troy was entirely fictional in a surfeit of skeptical zeal. By contrast, Atlantis was always fictional; the ancients themselves could find no evidence or tradition of its existence (though some believed it real), and only Victorian pseudo-scholars invented the myth that Atlantis had a factual grounding.
So, in sum: Schliemann didn’t use a map drawn from Homer to find Troy (though Maclaren did), and the entire claim that Troy was mythical was merely a modern fiction that had received repeated challenge even in the century when it was believed. Finally, Troy’s reality could be demonstrated from several interlocking lines of evidence, including multiple ancient texts, a cluster of archaeological sites and geographic names tied to Troy, and (later) Hittite evidence documenting a relationship with Wilusa, believed to be Ilion, whose oldest name would have been Wilion before the Mycenaean digamma (“w”) fell out of Classical Greek. Again, Atlantis has none of this.
So, if you want to argue that Atlantis is real because Troy is, then you need to get in your submarine and go find it, since no line of evidence provides for Atlantis any of the proofs used to determine Troy's reality.