What if Gendry Attacked Kings Landing?

Hear me out What if Dany legitimized Gendry before the final battle at Winterfell? Then, since Cersei didn't send her forces to help, Gendry went south, maybe with the Onion Knight and the Hound (maybe Jamie too) and rallied the knights of the south who bent the knee to Dany and any of the other southern houses that didn't support Cersei. Cersei has no real claim to the throne, she's just the only person there. If a legitimized son of Robert Baratheon showed up, with his war hammer, ready to overthrow a woman that every kingdom hates. I think the southern lords and the common people would follow him, even if he was just calling himself Lord of Storm's End. Then, in the show, we could have had a battle at Kingslanding happening side by side on scene with the battle at Winterfell.