Id be happy to weigh in and maybe help.
My comic reached 1k subscribers in about a week. I had not been promoted at all- My subscribers came from people checking the recently updated tab on webtoons. I did not cross promote on any of my social medias, I thought my comic was kind of embarassing honestly and kept it a secret except from some discord friends.
Its been a month and a half since I uploaded my comic to webtoons and i'm sitting at 50k subscribers, and Ive been promoted four times in rising star, hot today, fresh picks, and discover recommended.
-my comic is not in color. Ive gotten maybe 6 comments out of a few thousand asking for me to color it, and far more complimenting my choice to not color. What matters more than anything is readability, imo. Comics with art that is too overdone (full on painting) is just as hard to read as super sketchy and messy comics. Make it easy to read, the reader doesnt care how long/short it took you.
-webtoons readers NEED the vertical scrolling format. I have seen tons of great comics in the manga format absolutely flop because the readers dont like it. Space our your art. I was someone who went in intending to do manga style pages against my better judgement, but when i opened a comic in an app on my phone i instantly understood why i needed to use the long scrolling style. In the end, i much prefer it, i can get out lots of story with less time spent drawing.
-your thumbnail, title, and description MATTER. My title is "im the grim reaper", the description is "a girl makes a deal with the devil to become the grim reaper. As long as she delivers him the souls of sinners, her sentence in hell will be postponed." The thumbnail is her face. Its simple, to the point. You know the plot just from the title. A huge problem I see is people want to info-overload their readers with weird terms and giant plot summaries... no. Keep it simple. You dont want the reader deciding that the comic isnt for them because they get the entire plot synopsis on the description. You want them to only get so much information so that theyre curious enough to click on page 1.
-adding onto the point above, you need to have something waiting for the readers once they decide to read. Is your story funny? It better damn well make people laugh. I advertise as a supernatural, so right away the MC wakes up in hell and were on our merry way to killing sinners within 3 episodes.
-your art skill does matter, unfortunately. I dont think id have nearly as many readers if i wasnt at the level i am now. Story really DOES matter, but so does your art, and your art is usually what gets people to click in the first place.
-but even though i said the above, story is king. I met one of the webtoons staff at a con i went to a week ago and she remembered my comic immediately because of my story. 95% of my comics are story speculation. People love a good story, and i think there is a big lack of real story-driven epics on webtoons that readers are craving.
Anyway i hope this helps in some way. Ive been drawing for 15 years and this is like my 10th narrative series so Ive had quite a bit of practice, its not all luck. I hope you can find success in your comics.