Okay, I may be a bit confused on your ordering and stuff, so bear with me. I'm going to focus on critiquing your first three episodes (intro part1, intro part2, 3rd)
So the first thing I'm seeing is there is a lot of chaos in the words.You have a lot to say amongst these images, which will quickly overload your viewer for an intro. This sometimes leads to awkward placement, such as above. Your words should be centered between these two images. I recommend cutting down on the narration, leave it to the viewer to deduce how he's feeling from your word choice.
Instead of using these three pieces of text for narration, shorten it to something like "But apparently I wasn't good enough for heaven." You can see a good example of short and sweet narrative in the
first episode of SubZero.
Like for example here, you have some great illustrations that are doing a good job at expressing your story and the emotions the character is feeling, but you're piling tons of text on top. A single line above this panel that said "Though you desire to reach for the heavens, your energy is that of the earth."
In general, when creating a Featured webtoon, we have rules about how big the space between panels should be. I recommend you pick a value (Around 300 pixels is recommended for simple panel transitions, it can be longer for things that have godly narration in between or a scene change) and stick with it so your Webtoon reads consistently.
Like here you have a space, and then no space between the two panels. This reads quite messily.
After reading the first three chapters, I like how you were trying to show us the story though action, but it was kind of belittled by all the narration. You have way too much text, you should have probably 1/4 of what you had in the comic. It is a visual medium- Show us, don't tell us. If your main character is shocked about finding a user of the mysterious element he hasn't seen before, do not narrate in his head a whole exposition of the backstory of elements and stuff. Just show him slowly walking through the alley and maybe being like "This feeling..." "...Could it be? No, it doesn't feel like an element I've seen before..." Then show the guy surrounded in purple and all your viewers will instantly know the element is shadow.
Your art could use improvement, IMO at the quality featured desires right now you are a bit below it. I am confused sometimes though because some of your panels are quite good, good enough I could see them in a featured webtoon, but other panels are completely in the uncanny valley side
like the top face is excellent, but just a few panels down you have this close-up shot that falls clearly in the uncanny valley with janky lines (that is quite big, i could excuse it if it was like a tiny shot of him in the background looking wonky)
I think you should focus a bit on improving your artwork, or at least, taking more time with it. A Webtoon original expects the top-face quality in every single panel. I think you have a good idea how faces and bodies work in certain angles, but you haven't studied figures and faces extensively to know how they work thoroughly.
Practice doing studies like these. And do quite a bit of figure drawing too.
As for the story, as you already stated, you don't have anything crazy new but I don't know if there is a Webtoon that has this story. However there are a lot of stories in YA novels and TV that focus on elements, and I don't know something popular having a similar story would effect choosing a webtoon to be featured. I think your story is solidly on the middle line- It will not detract from your chances of being featured, but it also will not add to your chances of being featured.
Anyway, good luck ~