Mute Whilst this is still true a year on from the time of your comment. I'm going to say that the quality of stories to this site's catalog has improved due to the fact there are more native English speakers posting stories here.
You're not going to find a 100% grammar error free story posted here, since most of us are using this place to post our drafts and gain feedback (hopefully) as we go.
I think the quality has probably improved by 85%, although it's still a task of digging for a pony to find that grammatically well written story.
Grammar aside, I think the Romance category needs to improve on its diversity as there are too many versions of common tropes in Webnovel's catalog. That is another area of discussion of whether to write to the trope masses appeal to in this current day and age or go out on a limb to write something different to be classified as original.