As an author who's gotten really mean reviews, I can sort of understand why web novel put that review system in place. I used to have to mark, on one of my other counts, that it was abuse and web novel would come along and delete it after a few days. However, usually, those reviews were really not motivating, and some reviews even made authors rage quit because they were so insidious and frankly sometimes untrue. However, I'd also like to add that authors should let constructive reviews remain if they seem relevant, thoughtful, and not destructive.
Frankly, each author's page is like their brand, and what is on that page really matters for their future success. Many lawsuits have been won over people maliciously targeting businesses with bad reviews with money being rewarded to the defendent - or in that specific case the store.
On amazon, I've seen the power of one review on some novels I'm familiar with, and a single bad review can cost an author thousands of dollars. I frankly think that web novel is just trying to protect its authors by giving them the right to delete hurtful reviews.
To be honest, the reviews on this site have also gotten a lot nicer because of this new system. If everyone on this website was nice and constructive before hand, and didn't leave reviews like "Dumb... dumb... dumb... dumb... dumb..." this wouldn't have happened.
If anything, it finally gives authors the ability to defend from the sort of thoughtless reviews that were taking place. Also, not a lot of authors are like the author you described and many keep constructive reviews. I would just think of this new review system as better for author's productivity. It was so hard to write before and deal with these surprise reviews that were just plain mean.
I honestly think webnovel has improved because of this system. However, I do agree that authors should maybe have to give a reason for why they are deleting the review to you as a courtesy.