I left ARR and HW at certain points for the same reason. Grinding tomestones over and over just gets very boring for content after a while. Fates are obsolete at max level because they only give grand company seals. Hunts can be fun, but also quite frustrating, and hitting the raids or dungeons over and over just wears you down after a while. They need to mix the formula up. My suggestion is if they want us collecting tomes then offer a small amount of tomes from other content like fates or the challenge log. I say Fates highly because I see so many people not doing them. Make it a drop you can get that you can turn in for tomes or to purchase materia. One token gets you 5 or 10 tomes. Then 5 tokens gets you the items you use to purchase level 5 materia while 10 gets you the item for the level 6 materia. Another incentive to do world content.