From personal experience, I have completed my atma weapon, and on book 3 of 9. I really have no issue with the time sink, but I think the biggest issue is whether or not the months of farming are worth the investment. Here is why I say that.
Currently, collecting Atma can take as long as a week, or done in a few days depending on the speed and RNG factors. For books, farming 1 book and completing its pages a week will still be well over 2 months. The big question is, will the final form (not animus) be worth the time sink?
In 11, your months of time sink for Relic, Mythic, Or Empy weapons was a great damaging weapon, with a special weapon skill and other unique modifiers. In 14, I'm afraid a Zodiac weapon (Granted more of the quest will be added in 2.25, so even more to do for the weapon) will be of lesser strength or equal to a High Allagan Weapon.
It's easy to say the zodiac is for more casual player base to work up to, since some have no access to coil, nor have the knowledge to even attempt turn 9 whenever that day may be. But therein lies the problem. Compared to the speed of your first relic, it will more than likely be in the same situation your previous relic was, weaker or on par to a High Allagan. No unique stats, no top of the line weapon that exceeds Allagan. Its just a more drawn out version of the relic quest.
GRANTED I cannot say for sure what the final iteration of a Zodiac may be, seeing as it's not even released yet. But I feel the time sink invested into zodiac weapons may just be for a slight boost in stats equaling a High Allagan. It Destroys the purpose of what a Relic was meant to be. There is no disputing t9 victors should be given a great reward for thier efforts, but the investment between the two seems disappointing. I think if the reward in the end seemed more appealing, more players would be excited to finish it, instead of farming levi for i100, and just using that for the new coil.