I haven't really started going all out farming for Atmas yet (only have 2/12), but I think the system is pretty decent if you consider it as a time sink system design for ONE weapon for your main/first alt only.

Putting that aside, if we are to consider doing multiple Atmas, I think they should either:

A: increase drop rate of Atma
B: reduce mytho cost per book, probably around 800 ~ 1000 mytho each

and things will be pretty balance. Hell, I wish they will just increase the overall amount of mytho we earn from the game. It's not even funny how little mytho we can get now unless we can do every single duty roulette nearly everyday. Unless SE wants to cut majority of the players down to focus on one main job only.