Yeah, pretty much everyone hates the Webtoons rating for this exact reason. I got bombed by somebody (or possibly a group of people) and was stuck with a low rating for ages. Even with friends dropping 10s on me, I think on Webtoon I still only have like a rating of 6. I don't think I know a single person who hasn't had some petty or bitter little arse decide to drop a 1 on them for basically no reason, like it's even happened to friends with huge followings.
It's a bad system because it doesn't effectively indicate the quality of the comic. It doesn't show how many ratings or the ratio of high to low ratings and it's way too easy for people to just drop a low rating and go without needing to explain themselves in a review. Every time Webtoon ask for community suggestions, loads of people ask them to get rid of it, but they never do. 
Just one of many reasons Tapas is my preferred platform.