Who said he is going to keep fighting? He's up against CP0 and Seraphims, now we know that if it was Shanks, Kaido or Whitebeard, they would have fold them, but Oda doesn't care about Luffy's status. He clearly gave him G5 so that it's easier for him to mess around, the probability of him losing in the next chapters isn't farfetched regardless of his max level.