Yeah, certainly would need something to make it more condensed for people with lots of books.
Perhaps if it only showed the first three entries for every row, having to click a row to see which books it contained in detail, and had a search function to find individual books? 
I feel like for the view of all rows I’d be fine as long as it was scrollable.
Personally I’d say let the user grade however they like, placing a rating 50 book all the way at the bottom if they want, and just decide what to do with that info in the background. (e.g. ignoring some of the individual comparisons if they’re too far apart)
Couldn’t the actual grading system stay the way it is for now, but only the interface on the user side of things change?
I.e. through some algorithm pick only a number of pairwise book comparisons that are taken into account and handle the rest as extra gradings?
