[Neus]

They are and aren't the same as Black Beast's drop rate, because a Black Beast only has a book in its drop table 25% of the time. Bosses always have the catalyst in their drop table; level/10 is the rate. So level 60 bosses have 6% chance, which is the same as a Black Beast if it has a black book in its drop table. So the average drop rate of a Book per battle is probably around 3%.

I could bump up the drop rate on the boss catalysts a little bit but they're supposed to be relatively rare. Maybe 1% per 5 or 6 levels (12%/10% respectively).