Okay first my thoughts about deleting reviews:
Reviews are not primarily there to help authors. They are there to help other readers deciding what to read. If I read your first three chapters and your novel is absolute shit I should be allowed to tell other readers that, so that nobody else has to read this abomination. You want to tell me the novel gets way better later? If you are so capable, then fix your first chapters! If you are too lazy to go back and rewrite them, then you deserve the 1 Star review.
I agree that the exp for reviews has to go. A lot of people choose one novel they like and write a 5 Star review every day. Hell I do it sometimes. The character minimum does nothing to help either, as most reviews are someone smashing his hand on his keyboard a couple of times to get to the limit.
A review system is pretty easy to implement, with no cost to Webnovel! (Now they are listing ;) )
Simply get rid of the exp for reviews and make a new tap for "moderators". A bot randomly chooses people with a high activity, long time being on the site and similar criteria and gives them the moderator status. They can earn exp for reviewing the reviews. Maybe 10 exp per day for deciding on 10 reviews. There is an app called "Jodel" in Germany that does exactly that and it works extremely well.