From Doctor:

More number crunching:
40 runs of the chest gen produced 101 Tomes, or an average of 2.525 Tomes per Chest when lowered down to a weight of 10 from its base weight of 30.

Should we just give it its own pool for its stuff maybe? Either way I'll make my setup on 1.19 Quark and compare it to that

On 1.19, I had 88 Tomes for 50 Generations, or an average of 1.76 Tomes per chest
1.19 -> 1.20 is about a 1.4 times increase, even if 1.20 is the one at a weight of 10.

Did some research on this:
10 rounds averaged 2.8 Tomes, which whilst isn't as much as shown here, is more than triple the amount of average enchanted books (0.9)

Of course, a larger data set would probably be better, but the numbers need to be bumped down a fair bit

Correction:
All runs were at a weight of 30, I'm just an idiot and didn't realize it was a config thing

Alright so in short this is an issue with the default config value being very high. As for why it seems like the amount has doubled, I couldn't find anything that would correlate to it, so I don't THINK this is symptomatic of more loot issues, but we will see as we continue. I'll let Vazkii decide on what to do from here.