FATE's are entirely optional. You do not have to do them. They are the fastest way of gaining exp currently, but they are also mindless and boring. If efficiency is all you care about, then FATE grind. If however, you'd like to actually have fun playing the game, go do dungeons with friends, or leve quests, or grind out some mobs that drop stuff worth gil while leveling your chocobo, or whatever else you find entertaining. There is no race to 50.

You are not forced to FATE grind. I've leveled two classes now on strictly dungeons, because I enjoy them. SE has given you an option for faster leveling, without it we'd hear non-stop complaining of "Why do I have to do dungeons to get exp /sadface, I want to exp solo /tears". The complaining won't stop with the boosted dungeon exp either, because MMO players are fickle. You don't even know what you want.

FFXI had slow leveling and people complained. FFXIV has fast leveling and people complain. Dungeon exp is still "fast enough", but ya'll like to whine.

Take your time and enjoy the game.