
1. S1 Hyo-un was not his true self. He was suffering from a life threatening illness unique to his kind and was suffering heartbreak trauma on top of memory loss. He also couldn't trust Taehyuk till his memories came back. After his pearl was restored, along with his memories and the love of his life, his true personality came back, which was always a giant dork who was absolutely smitten with Taehyuk.
Him calling Taehyuk "sir" is akin to how they call someone older that's a friend or close acquaintance "hyung/noona." It's a respect thing.
2. I stated this waaaaaay back at the beginning of the flashback; Hyo-un looking like an adult while being abused would not have had the same impact on the reader. Humans tend to feel more empathy for children than they do adults 'cause of the power imbalance between the child and the abuse happening to them. Besides, Hyo-un is a dragon. His physical form holds little significance since he is supposed to be a powerful, immortal creature. He isn't human and clearly didn't age like one at all. His development is tied closer to the power he gains than how long he's been alive in human years. He could have taken the form of a decrepit old man when he first woke up and it would still hold 0 meaning age-wise.
3. It was Taehyuk's brother that was in love with him, not Hyo-un. I'm guessing this part is just a typo so I won't say more about that.
4. Once again, if it was some random side character and not Taehyuk's brother that was obsessively in love with him it wouldn't hold the same impact. We woulda just seen him as meddlesome, irritating at worse. Knowing that they are blood related only drives the level of disgust and horror higher in the reader. It was shocking before finding out it was love which made the reveal revolting. It made him into a more sinister villain ((in their past lives. He's barely even there in their present lives due to him not wanting the same events unfold)) rather than a stalking horse for the main couple.
It's fine if you don't like the themes or tropes used in the series, but to say it would have been "better" without them is just you speaking from an opinionated perspective. The story is fine and honestly one of the best ones I've read where reincarnation is concerned. It's not the artist or writer's fault if the themes they use to tell their story don't sit right with you when there's nothing wrong with what they wrote.
Mourning the loss of the greatness that this story could have become if they kept hyoins personality from season 1 and the backstory wasnt as weird
If we had hyoin s1 personality the entire story (because his s3 personality was so different and after a while the sir got real annoying) + taehyuk taking in hyoin as an ADULT form and bringing him back to good health and they fall in love like dat + hyoin having a childhood friend be in love with him and nawt his brother
GOD TIER I TELL YOU!!