To put it in perspective

S ranks gave 200 myths, A ranks gave 80. It'd take 8 S ranks or 19 A ranks to get enough tomes (1500) for a book.
S ranks give 50 Solderily, A ranks give 20. It'd take 10 S ranks or 25 A ranks to get enough tomes (500) for a book.

Dungeons and Trial roulette are mostly the same....mostly. All of this stems from *gasp* hunts being overpowered in rewards >_>