The dura...

When spellbooks came out they were incredibly durable. I remember dueling with a 5-dura palala pre-g16, treating it as a shield normally is. It took a week to break that. However when spell book repair quills came out, the things suddenly became extremely fragile, I broke a 5 durability book in an hour of regular use.

I checked the dura loss and it took me less than 15 hits to break a single durability on the spell book whilst blessed. And this is a 30 dura book. I checked a friend's HEM via [unstated methods totally legit pls no sue] and the result came up the same. The durability loss was insane.