1) Paladin's magic mitigation certainly doesn't help, but it's not the reason I don't use paladin in 3/4. Paladin's garbage utility doesn't make up for its downfalls.
2) Dark Knight probably needs a couple changes to help them match the frequency at which paladin and warrior can mitigate physical hits. Basically, I think if Reprisal was a guaranteed parry (like Sheltron) that counterattacked with the current Reprisal, they would be fine for any physical buster that might come in the future. Maybe throw in some extra parry power while using it.
3) Jobs being bad for 6 months at a time is stupid and so is niche tanking.