To be honest, I thought the sequence and timing-of-events was perfect. The viewers got their brief post Hinokami Kagura emotional high with Episode 19 and Rui's fake death, and that Form 11 non-fight was perfect for Giyuu to showcase his powers (which he won't get to do all that often as the story evolves rapidly and the primary protagonist become incredibly strong, thereby needing no rescuing). Tanjiro beating a lower moon on his own would be a bit too much at the stage wrt. power scaling, even for a shōnen — and none better than Giyuu to finish the job...considering he spared Nezuko's life at the very beginning when he could've easily terminated both her and Tanjiro, is a former pupil of Kamado and also a friend of Sabito — in a lot of way's he's like an older brother / guardian in spirit to both Tanjiro and Nezuko at that point in the story (and even vouched for them using his status as a pillar, when many of the rest were opposed to them joining the Demon Slayer ranks).
Yeah I said earlier I understand the logic of the mangaka and actually don't disagree with it for the sake of character development, showing the power of the Hashira and that Tanjiro still needs more training. My only complain was the fact Rui cut his head on his own kinda felt, I don't know, anti climatic? Maybe the mangaka didn't find another route for him to survive. It is not a big problem though. The fighting sequence in episode 20 and 11th form was as hype too.