I think prose works either way, bc I feel like dialogue vs. descriptive isn’t necessarily as clean-cut as easy vs. hard (or hard vs. easy). There are times where the dialogue is easy and makes it go quicker, which would make it easier, but then there are times where there are multiple characters talking and/or it’s difficult to tell who’s saying what, which would make it harder. Descriptive writing gives you more context to work with, which is why a lot of people find novels to be easier than manga, but depending on the author’s style, those sections could be more difficult than the dialogue. More dialogue could also make it pass quicker by inflating the page count, while more description takes up more page space. It could also depend on what someone’s used to reading
Speaking of manga, actually, I guess it could have “text density” rather than “prose,” with “sparse” on one side and “dense” on the other? There are manga with more narration etc. than others, but I feel like the text density plays a bigger role in difficulty than what percentage is dialogue
If each of these is optional the way the separate entertainment and language-learning star ratings are optional, that would be nice too. I get the feeling I wouldn’t always be able to accurately judge all of them for every book I reviewed, but that wouldn’t mean I wouldn’t be able to do at least some (e.g. grammar. I don’t pay attention to the grammar unless there’s any I struggle with, and that doesn’t necessarily relate to how advanced the grammar point is)
