I don't understand this whole "reading level" strata system, and I think some people on here are weird about it. What's your take on words you don't know and its correlation to reading level?

Ok, so for context: I haven't really read a lot of full books until now, but I've read bits and bobs of lit whenever and wherever I can. This makes me incredibly insecure as a new "reader". I'm currently reading Wicked, and it's full of words I don't know as an adult, even though I have a learning disability that makes me good with words and vocab retention (NVLD).

Anyhow, Wicked IS A 6th GRADE READING LEVEL. Some people on here are like "if you don't know a bunch of words, it's not your reading level". Ok.....I didn't graduate high school and move on to higher ed to be told that. Did I get by reading books? No, so maybe I am an illiterate dumbass, I guess. I graduated by the skin of my teeth, thanks childhood trauma (college was better though).

I GET the story and use context, but Wicked is not baseline vocab (unless it is to these reading level people). Am I crazy, or should I know the 6 words a page that I didn't retain because I'm living my life? Is a grown adult who doesn't know the 5 words per page unable to read Wicked?