Of all the known members of House Baratheon in the show they are all dead. So that leaves us with whether or not Bastards have rights, well that isn't a clear cut case as GRRM has said before.
What if there are no childen, only grandchildren and great grandchildren. Is precedence or proximity the more important principle? Do bastards have any rights? What about bastards who have been legitimized, do they go in at the end after the trueborn kids, or according to birth order? What about widows? And what about the will of the deceased? Can a lord disinherit one son, and name a younger son as heir? Or even a bastard?
There are no clear cut answers, either in Westeros or in real medieval history. Things were often decided on a case by case basis. A case might set a precedent for later cases... but as often as not, the precedents conflicted as much as the claims.
Westeros, So Spake Martin, The Hornwood inheritance and the Whents
However, Gendry is also an unacknowledged bastard of Robert's so wouldn't really have been in the line of succession and thinks so himself. And in the show bastards appear to have less rights of succession compared to the books, see Ramsay Snow for example.
Daenerys: Gendry. That's right, isn't it?
Gendry: Yes, Your Grace.
Daenerys: You're Robert Baratheon's son. You are aware he took my family's throne and tried to have me murdered?
Gendry: I didn't even know he was my father until after he was dead.
Daenerys: Yes, he's dead. His brothers are too. So who's Lord of Storm's End now?
Gendry: I don't know, Your Grace.
Daenerys: Does anyone? I think you should be Lord of Storm's End.
Gendry: I can't be. I'm a bastard.
Daenerys: No, you are Lord Gendry Baratheon of Storm's End, the lawful son of Robert Baratheon. Because that is what I have made you.
Game of Thrones, Season 8 Episode 4, "The Last of the Starks"