The small amount we know of the original timeline show how an annoyingly clingy child was ostracized, targeted, and turned into a human experiment. This information did nothing to mature the MC. It simply caused a deep instinctive disgust for the guy he used to cling to.

The potential for character development here is in the distinct gaps the author never fully explains. The og!MC is apparently a top who didn't have a good initial impression of the og!ml. He was in fact not nearly as annoyed at the cannon fodder as presented. Most of the other characters disgust for the MC were led astray by the attitude of the og!ML toward him. The admiral is not really mentioned. It can be easily guessed that he broke down without the MC's support. His family lashing out so strongly against old friends doesn't make much sense, so there could be more backstory here.
The ML finds out his connection with the MC as his lifesaver (gets news morning after the birthday/estrus in new timeline) only after the estrus incident (trying to climb into og!ML's bed in old timeline), unless that rotten peach blossom adjutant found a way to suppress this news. Regardless, the family doesn't know the MC can improve the ML's illness, so they can't really lay blame on him for asking to switch the marriage candidate to the childhood friend of the same family? Being angry he made an attempt on the nephew who has been leading him on for decades doesn't really justify destroying the MC's fam. We know that this let the og!ML snag MC as a research material, so perhaps he instigated some things after realizing the MC might not be a normal human. For example, taking advantage of the rumor that the ML's injury was caused by a mermaid in order to persecute the mermaids next door.

My theory is actually that he was stimulated to realize that his lover and his uncle started to pay attention to his little follower and he panicked. "No one else can have what he doesn't want" fits his personality considering the way he panicked in the new timeline when he realized MC stopped paying attention to him. He obviously doesn't like the MC very much even if he showed strong interest in the changed MC. It was more that he couldn't handle losing the MC's affection even if he didn't want it. It was his to look down on and throw away. Bro seems to feel far inferior to his uncle and tbh stepping on the MC is what gave him capital to be so proud. The confidence and face he had thanks to the MC paid a large part in his popularity, shown by the sharp drop once people realized the MC's change. He is so twisted. The MC's identity is a huge hidden danger. Luckily, the MC's ability to conceive apparently will not make him stand out very much in this era considering no characters thought to drop the marriage contract for this reason.

"Lu Chengze grew up with Song Huai and knew Song Huai very well. He was just a young master who grew up in a honeypot. He can't be said to be bad, but he is very dull, small-minded and have many bad ideas. He always likes to do something s*upid to attract his attention. Anyway, he just a pretty s*upid vase." (Chapter 14)

physique.

one other thing I disliked was that every time the MC and ML did anything it was was the MC was drunk or in his estrus period which I feel was like left out, because they never did it after the MC drank the mysterious fruit whine stuff and then after that thing they never talked about it again??