I haven't seen anybody mention this:

Have you wondered WHY fate XP is so high? Have you wondered why Yoshi's answer is to add more XP to dungeons???

The answer is that leveling to 50, in Yoshi's eyes, is a throw away portion of the game. When you're asking for fate xp to be nerfed, you're actually asking that the entire game design move in a different direction - one opposite to what Yoshi has laid out. Its never gonna happen. I too think that leveling in this game is way to fast and would prefer more of a journey to 50 than a mad rush. But the game is designed around being level 50. Asking for fate xp to be nerfed just isn't that simple.