Just as a point of clarification, the idea that there 'is always something behind a legend' and especially, that legends/myths/folktales refer to a great person in the past is called Euhemerism. This takes its name from the Greek, Euhemerus (4th cent BCE). Many have taken this approach over the millennia, either inspired by Euhemerus or simply falling on this approach coincidentally. Snorri Sturluson, the thirteenth-century Icelandic writer, for example, imagined real people to be the source of inspiration for the Norse gods. The practice continues with efforts to find the 'real Arthur' - as well as his court.

All this is not to say that there can't be something real behind a legend/myth/folktale. It's simply important to remember that these narratives can emerge without something behind them, and even when there is something behind them, they are prone to such dramatic wandering that what was behind them (if anything) is largely irrelevant and unrecognizable.

There are also efforts to diagnose the function of elements of folklore. It is an interest exercise, and it can yield insight, I suppose. But it isn't unlike literary analysis. Sometimes the thoughts of an authority discussing what is behind a Shakespearean plan can be inspiring and it can increase its enjoyment. And sometimes it is merely the musing of someone who doesn't know squat about the play. It can be hard to tell the difference, except in one's subjective reaction to the analysis. And there's the problem: an interpretation that is subjective at its core and can only be evaluated on a subjective level, is at its core, ... well ... rather subjective. It can be fun, but we can't confuse it with objectively demonstrated arguments based on facts.

I hope that helps. Others can certainly dive in - the water's fine and not too deep.

An additional note: you may find it useful to see how I am handling just this sort of thing in my manuscript; The Folklore of Cornwall: The Oral Tradition of a Celtic Nation. I'm in the process of completing my final edits before it is passed on to a copyeditor, and I just stumbled onto something that's akin to your question. In my chapter on giants, I deal with interpretations that attempt to find hidden messages or buried meaning in oral tradition. Here is a paragraph:

A subject as impressive and widespread as giant folklore often attracts exotic interpretations. Brendan McMahon asserts that Tom the Tinkeard ‘with his wheel and axle recalls images of the ancient Celtic sky gods, an interpretation that reaches back to the dawn of European thought.’ According to McMahon, Jack in his hide coat conjures the image of the ‘sorcerers depicted in the caves of Les Trois Frères.’ He also employs a Freudian interpretation, drawing on the story of Oedipus, to understand the typical storyline of the hero slaying the older giant. In another attempt to understand Cornish giants, Paul Manning includes a discussion about the supernatural beings in his article on knockers. He suggests that giants represent agricultural society while their foil, ‘Jack the Tinkeard’, symbolizes the tin industry. This is part of Manning’s attempt to see the ‘Jewish’ knockers of Cornwall as representative of the capitalistic mining economy as opposed to the consumer-based agricultural society. Since these sorts of connections and interpretations cannot be proven wrong nor verified, they do little more than inspire speculation.