A solid point: books may excel at one dimension while not even attempting another. I suppose one might have to ascertain what genre, exactly, a book falls in, and how it fares in its own genre. But then you're not comparing pairwise, and we lose the benefits of our visual cortex or whatever neural system is so good at pairwise comparisons.

Constraining pairings within their genres might suffice, if possible. There are several standard ontology for books, and it's not a trivial problem.

I don't think it makes much sense to compare a fiction book to a non-fiction book. There's not enough points of comparison. While both can be compared on quality of prose, the fiction might be judged on characters and plot, and the non-fiction book on accuracy and detail.

You might as well ask the question: Who is the better Tennis player? Roger Federer or Garry Kasparov?

A system would need to draw some kind of boundary conditions so you are comparing things that have more in common than "printed on paper and bound".