Just sounds like you were having bad runs is all. Maybe you executed mechs properly but your party members didn't? It's easy to drop if your healer's not healing and/or dead.

As for fates, depends on what kind of fate you were doing too. Also, how well is your choco healing you?

Like Vahlnir said, PLD does a pretty good job defensively at lvl 50. Heck, just having access to HG at that level--and doing duties in that level--gives it a slight edge over the other tanks.