Not true regarding the Hound. He was elevated to kings guard when Barristan Selmy was relieved of his spot. The Hound just refused to be made a knight.Sam also fits under potential heir as Warden of the Reach. And Jamie (older brother) is warden of the Westerlands (now that Cercie relieved him of his kings guard obligation).
And the hound was never an official kingsguard. Or even a knight for that matter. But he was Joffrey’s personal body guard whatever that makes him.
And if we’re listing wardens of the cardinal directions that have potential ascension to the throne, Sansa is Warden of the North as Lady Stark. Her claim would be higher than Sam’s (as a lesser lord); unclear if the North is before the West/Jamie.