There are numerous aspects to leveling -- fates, dungeons, leves, guild leves, grinding. Where there are five methods and one is out-of-balance, you reduce that one instead of raise four. Balancing levels is almost always done by reducing the contribution of one area. It's hard to argue that the experience gain in FFXIV is too slow in general.

It's simply a practical matter; nerfing is better. Not childish.

FATEs are great fun, I've had a better time chatting with people there than running dungeons, but it doesn't seem to me like FATEs create a challenging and nuanced gameplay. It's more akin to a swarm of locusts. I like the challenge of tagging mobs when I have few instant cast spells and competing to get gold, but when the gameplay actually implies that a white mage should cast stone instead of cure, you have to examine whether FATEs are an aspect of the game worth rewarding.