I agree that the whole ranking system thing can seem a bit artificial, but for the sake of being contrary I'm going to say that it isn't all bad.
It is is simple, since not too much thought is needed to grade a book (so long as you've read more than one book in your life

). This is both a strong point and a negative one. Anyone can express their views in it, which is good and bad depending on how inclusive and friendly you feel like being on a particular day.
It might be possible to construct a more complex survey with multiple lines of enquiry. You could have a poll asking which books have the most creative background, show the most ingenious use of language, contain the most interesting and versatile characters, have the most engaging conflicts, the most insightful observations about people... you get the idea.
It would be a bit complicated, although it could be done. Some people might be turned off by the length of time it took to fill out the form but that would be the cost of business.
Of course going to an extreme some people don't like quantifying
anything, especially creative works; to which I would admit that surveys are only rude approximations - but they are the best we'll get.