Distance is an important element of the design of a story. In some cases you want the story to feel very intimate, as if the reader is right there with the protagonist, in their thoughts, in their immediate present. This is the most fashionable way to write today and it is reflected in the overuse of first person in contemporary narratives.
In some cases, though, you want to establish distance. You want to separate the reader from the protagonist and their experience in time and in space. When Star Wars begins "Long ago, in a galaxy far far away," it is establishing distance.
There are a number of reasons to establish distance in a story. One is to inject a sense of the fabulous into the story (without necessarily straying into outright fantasy). None of the droids in Star Wars perform any useful function. Why, in heaven's name, does Luke's starfighter not have an onboard navigation system, but instead has an R2D2 shaped hole in the back? Imperial walkers make no military sense at all. Why is there a planet inhabited by teddy bears? There are no moments of stunning psychological insight. It is a romp, and the distance established tells the viewer, don't sweat the details, just enjoy the show.
The word "legend" signals distance. The use of first person signals intimacy. They pull in opposite directions. More importantly, perhaps, legends are a literary form that depend on establishing distance. If you have written an intimate story, calling it a legend is perhaps a mistake. If you have written a legend, telling it in first person is perhaps a mistake.