Every user of Calibre has THEIR OWN ideas of how they want their metadata.
I could care less what YOUR (or anyone else's here's) Rating
(None of my sources have that ticked.
I think it stupid to include the tag Fiction along with a tag Science Fiction
(Actually, I only use Fiction as a tag when I have no idea what to classify a book that is not Non-Fiction)
I also combine the dozen permutations of Science Fiction
into its root , Science Fiction.
Metadata is like Religion, (BTW MR requires discussion of those to be done in the slightly hidden, Politics and Religion forum), a volitile topic