While the Crabfeeder had been set up as House of the Dragon’s first big villain, he was killed by Daemon Targaryen within the same episode that the war was first shown. After receiving a letter from Viserys, Daemon marched into the Crabfeeder’s territory with an entire army attacking him and killed the Crabfeeder in one-on-one combat. Daemon exits the cave with the Crabfeeder’s head, chest, and one arm dragging behind him to prove his victory, implying he used Dark Sister to finish the war. The sequence of events felt oddly fast for Game of Thrones, but in reality, the War for the Stepstones had already been fought for three years. The time jump skipped over the growing rivalry between Daemon and the Crabfeeder and Daemon and Corlys’ many losses, leaving only the development needed for Daemon to finally win the war. The Crabfeeder’s importance in House of the Dragon’s story was also only as a vehicle for Daemon’s character development. Daemon needed a villain worse than himself who he could triumphantly kill to prove his worth to his brother and the realm – the Crabfeeder himself was largely irrelevant. Since House of the Dragon season 1 has a lot of ground to cover in only a few episodes, the Crabfeeder’s death needed to come sooner than later.
Considering the Crabfeeder’s overall purpose was to exhibit Daemon’s valor and triumphs outside of King’s Landing, House of the Dragon leaving out the moment that Daemon sealed his victory is somewhat surprising. However, the important part of Daemon defeating the Crabfeeder wasn’t to prove his physical strength in a duel; it was far more necessary that House of the Dragon episode 3 dedicated screen time to Daemon risking his life without hesitation by walking straight through flying arrows to face the Crabfeeder in a duel.
As has been the case in House of the Dragon season 1, this battle wasn’t truly between Daemon and the Crabfeeder; it was between Daemon and Viserys (or really, himself). Daemon needed to prove to Viserys that he could fight a battle and win all on his own, demonstrating his worth as a “second son” and finding power on his own accord. Daemon running through the Stepstones’ battlefield had already proven how intent he was on ending the war there and then, and there was no question that when he followed the Crabfeeder into the cave, Daemon would come out victorious. The important moment to depict on-screen was the aftermath in which Daemon walks out with the Crabfeeder’s head to reveal he won the war, which was still extremely effective in implying how Daemon killed House of the Dragon’s first villain.