Books, music, and all other art forms, unlike apples, are not fungible, not even items of the same "quality" (however defined).

A point which applies equally to old and new. And ultimately every choice comes down to read or don't read...

Yes, no-one can read/listen to/view more than the tiniest fraction of what there is, but to read nothing old, or to read nothing new, are selection rules that have only simplicity in their favour. There is no one-dimensional scale of "quality".

I think you're deprecating them too quickly. Let's take the 90% guess at face-value: if you are selecting primarily from just the most recent 10% and quality - however multidimensional you choose to define it - then you need to somehow make up for throwing out 9/10ths of all the best books, the ones which happened to be old!

It'd be like running a machine learning or statistical algorithm which starts by throwing out 90% of the data from consideration; yeah, maybe that's a good idea, but you're going to have a hard time selecting from the remaining 10% so much better that it makes up for it.