Dragoon and Viper have more native HP and defenses than the others. Without even putting up a buff they will often survive things everyone else doesn't. And of course they have Second Wind + Bloodbath. Dragoon also has a heal on Life Surge, and Elusive Jump to assist kiting.

I just saw Keen Flurry as bloat. Especially since they aren't tanks so 99% of the time it's a waste.