In Game of Thrones Robert Baratheon rebelled against the Mad King and took the Throne of the Seven Kingdoms.
Doesn't this legally set the heir to the throne to the Baratheon family by right of conquest? Both Stannis and Renly claimed to be the legal heirs to the throne.
Since Gendry is the only son of Robert alive, this makes him the rightful heir of throne instead of
Daenerys or Jon Snow
However, this seems to be forgotten in the series.