Zelda is the original vidya fairy tale and it hasn't strayed far from that which is why it's succeeded for so long.
It's also held true to a core balance of three things: Power (combat), Wisdom (puzzles), and Courage (adventure). Thematically sound and consistent in its best entries and with each represented by a character archetype that's present in every mythology the world over.
It manages to capture all those in such a great balance so often and that's the reason why the formula works. Too many derivatives go too far in one direction and become Zelda-like but the something "off" is the balance.
Take Darksiders for example. Darksiders was too heavy on the combat. It had the other things (some puzzles, some adventure) but not to the depth of the combat, and it had a great comic book style but it wasn't that timeless fairy tale aesthetic that Nintendo often goes for. It went for heaven-and-hell politicking and eschewed the "hero slays dragon, defeats evil sorcerer by courage and cunning, saves the princess" motif.
Link is the vidya equivalent of St. George, or Beowulf, the first vidya mythological hero that isn't just an everyman mascot like Mario. His personality is in his deeds which are performed via you, the player, becoming that "link" that Miyamoto wanted with that name. Zelda is the pure, kind-hearted, wise but often naive virginal figure that is taken by the power-hungry figure that craves power for its own sake.
The incarnations may change but the characters remain largely the same, and that's to its benefit for the most part.
There will always be tellings of King Arthur, because it's an important story and timeless myth, and as long as there is vidya there will be tellings of Princess Zelda.