Most korean webtoons adapt from a novel, with a much smaller percentage being comic originals. Manga (particularly one shot volumes) on the other hand tend to be an artist's debute work. They illustrators primarily, writers second, and it's done to promote a healthy industry. But because there's so much manga being published per season, there's bound to be a pool of good and mediocre series, compared to a smaller webtoon pool per season which tends to be long running but not necessarily lengthy in total because of the format.
As much as I like certain webtoons, I have far more manga favourites. Evaluating quality by encounter is a really skewed take.
Honestly, more extended plots (mostly in BL and Gl) can be tedious. Before anyone says anything, I'm a One Piece fan, with more manga focus than anime. I can't wait for the remake of Fishman Island.
Anyway, sometimes it is not even longer, just sometimes the chapters are cut short. There are some manhuas that I like over manhwas, like Grandmaster of Demonic Cultivation; however manhuas can feel dragged out. And there are longer mangas that are fine and end well. It all depends on the quality of the work. Also, it is easier to get translations of manhwa over manga.
I know good long mangas, but the thing is that regardless of how big the plot is, it needs to be separated into chapters (average of 4 to 7 chapters) that will be structured in each volume. Of the mangas that I've read that are in webtoon format with more than 7 chapters, they didn't manage to structure the script well. They had a plot, postponed the plot and in the end resolved the plot suddenly. The rhythm of the work doesn't seem well structured.
I feel that Japanese authors are not very adapted to the longer plots that independent webtoon publishing brings. It is the third one that has a sudden and unsatisfying ending. As much as they have It brought interesting plots and captivating characters, but the ending sucks. So it would have been good if they had stuck to the good old bread and butter of publishing 5 chapters and 1 extra.