In my mind, FATEs are just like DLC. They're there if you want to do them, but if you choose not to, you don't have to do it. The Boss FATE are the most enjoyable for me because 1. Everyone get to participate in some capacity, whereas in the normal ones sometimes it's hard to even find and strike a target before it's dead. To say nothing of Healers in that regard. 2. They promote teamwork, and provide practice for Dungeons. the normal ones do this to an extent but since there are so many more PCs/enemies it can get chaotic. 3. I think they have the best 'story reasons' for being there. A single powerful enemy has appeared to wreak havoc however they will, and it's up to heroes(that's us) to stop them.
Gaming is not a race. Leveling is not a race. No one wins ALL the things for hitting level 50 first, second or 87,452th. If all you're concerned about if getting to 50 as fast as you can, where's the fun? The adventure? The thrill?