Honestly speaking this game is for casual players. Everyone can clear everything even with random groups. Killing a primal ex after 10 trys with mediocre gear is a joke. This cant be called end game. Thats where the long therm motivation fails. Killing everything on the 1st or 2nd day and getting all bis gear the week after is boring and unsatisfying. Thats why people leave until you release new content which is cleared after a few days again. There should be content for everyone to set a longtherm motivation.
A couple of ideas which improve the game by a ton.
1) aether shard: lets you enter expert dungeons with increased difficulty after clear with weekly reward the more aether you have collected. The higher the difficulty mastered the better the droprate. Rewards could be a pool of: mounts, materia, crazy transmog gear etc.
2) a third difficulty for: primal ex and savage mode.
3) Set gear bonuses from raidbosses.