Anyone hopes for retcon of events of manhwa in anime series?

I think it is just (mostly) you. There is a problem that SIU made ToG world too big for even him to handle. Its true that often the entire casts disappear only to show up 400 chapters later, and many people don't have a memory capacity to even remember them. There is also for sure an issue of his Korean fanbase rushing him to develop the main plot at the cost of continuous development of all sub-plots and supporting casts.

But it kind of makes sense in a big picture. In the "real world", people meet and say goodbye all the time. You are not stuck with your kindergarten group until the end of the world (except maybe a very few people). The world powers are comprised of many large factions, each with their own internal kitchen and politics. You can't hope to describe the big world with just a handful of characters to fit the chapter opening panel. Not with a such a scale at least. Just like GRRM spends hundreds of pages describing small things in excruciating details, or like how there are hundreds of characters in LotGH just to begin describing court politics between two countries - if you want something to look real, it has to be believable.

But not everybody likes this, of course. Many don't care about worldbuilding and just want a shot of shounen dopamine with simple and familiar cast of characters, and\or the straightforward sitcom pace of the plot.

I personally enjoy the depth of the world that SIU managed to create. I think the plot is okay, although it could be tied up better (perhaps the side stories for the groups that couldn't make it to the main cast power creep?). I like it how the large the world is, and when for example the Great Families are shown, you can feel that they are real large clans, basically entire countries in themselves.

As for the villains turned allies trope, I mean, you just remember those that did. There are still clear factions, and most of the side-changing happens within one faction (you know which one). Also most of the "main baddies" stay as such, even if it takes hundreds of chapters to establish it, especially that one you might had in mind writing this post.

@wolf-of-war I remember I wanted to watch Legend of the galactic heroes but that was at the same time as wanting to read Jojo and started the latter but finished neither. That about big worlds, the families and world building in TOG was exactly what I liked the most besides the original powers and concepts. For me the latter two just derailed and this became a contradictory and painfuly slow chase with some princess gacha at the beginning:


I love world building through showing what the characters are doing. Just that our characters can do less and less and I don't like Bam enough-