Well, I can tell you I have 150 reviews, with the lowest rating being a 3. You can come on discord and I can show you a screenshot film where I scroll down all my reviews history(the deleted reviews can still be found there).
The only reviews I deleted were spamming 5 stars and one 1 star review slandering me from a reader who hasn't read the story (and still hasn't) and was basically just accusing me of deleting reviews. And I have a screenshot of every review I deleted for webnovel staff in case of harassing or for anyone curious.
So yeah, stories with high rating exists(And I could tell you a few names) , because it also has a lot to do with the readers' profile of a story. Take Vampire System for example. Popular, but young audience. Fast paced, with common tropes so naturally not for veteran readers. 1st in ranking, but with many1-2-3 stars rating. The thing is, neither the 5 stars nor the 1-2 stars are fair rating. (not any novel on the app by the way, my novel is no exception) Because, a mature reader would find it too childish to read it, even less to bother writing a review (and if he/she does, the review would surely be kept because constructive, with an objective tone.), while the immature ones rant against or magnify anything they enjoy or hate. Some reviews are bordeline disrespectful if not clearly insulting while other will say it is the best novel they ever read and praise you like a genius. If you wouldn't dare to use the same tone in front of a real person in real life, then why should an author working hard to write a story endure them? It's not about ego, but self-respect.
Now, I don't say some authors don't delete reviews abusively/bot their way up ect.. and we all know them. We can't even mention their names in webnovel forum and the authors already reported them for naught. So clearly, it won't stop anytime soon before Webnovel decides to hire some moderators to enforce this instead of giving full power to the authors.