As far as I can see when I sort the list of comic in Discover by popularity, they all have very good quality to me. (And I personally follow and read a lot of them, although there are still some I don't particularly care for. And I think I know which webtoon you are talking about LMFAO They just update a lot. LIKE, A LOT. Several time a day, to the point the notification drive my friends nut she just turned it off. It might be sketchy but the plot still is interesting)
The variety in both story and art quality can also be seen on Tapastic's popular section to be honest.
When you look at Webtoon's popular section and Tapastic's popular section side by side, I think they are very much similar to me.
I have noticed yes the majority of them are around that age range, but there are still a lot of adult and late teenagers on there so ÂŻ_(ă)_/ÂŻ