I totally agree with your bolded line; in fact, it was the first thing that came to mind when I clicked on the title. I first heard it from V. E. Schwab, a very successful adult and Y.A. author, and the more I think about it, the more true it sounds. The important thing to remember is that readers are not writers--they are not critics. Their impression of the book, even if it was "x character was written so badly", is subjective. I've read some of V. E. Schwab's own reviews on Goodreads of her trilogy Shades of Magic, and comments on just one character ranged from "she is bland, flat, boring and badly characterized" to "I love her! She's my favorite character, and one of the most fleshed-out personalities in the books." (Not verbatim, just from memory.)
Something else that comes to mind are the Goodreads reviews on I Am Not A Serial Killer by Dan Wells. Many people gave it a low rating because of a certain plot twist a hundred pages in, and quoting one reviewer, "the rug is pulled out from under the reader". The top review claims that the book 'jumped the shark' and, quote, "This was a complete FULL STOP, WTF just happened moment for me that left me stunned and bewildered."
The problem is that the plot twist was not supposed to be a surprise. I read the entire book myself knowing that a plot twist was coming, and found the book telling me twice what the plot twist would be before it happened. Dan Wells knew that the twist would be huge, and so he deliberately softened the blow by explicitly stating "but what we didn't know back then was that ____" before the twist came (again, not verbatim). This is why what shocked me was the shock of many reviewers on Goodreads. If their eyes skipped over the line or they brushed it off and forgot about it, it is not the fault of Dan Wells or his book at all. Sad that he received so many negative reviews due to the surprise and confusion.
I don't know if I'll ever be publishing a book, but if I do I'll be taking a page from V. E. Schwab and only read the reviews by actual critics. Reader reviews aren't valueless, but they're worth much less to an author than another reader. Even then, I would take their contents with a grain of salt.