Dark Knight in all slaying accessories... please no..

[Delorean]

Because Warriors doing the same is okay?

And yes it is if you have the skill for it.

debatable

as a tank your survivability is pretty dependent on your healer's ability to, well, heal. if they are not good at healing damage as it comes in and have a difficult time predicting heavy spikes your survivability will decrease.

the worse your healer is, the more value vitality will have. i mean, it's still a pretty solid stat when your healer is good, but it is even better when they are awful because it gives them a lot of slack to work with. but depending on who you play with, extra vit can largely be a waste of itemization, becoming a sort of optional comfort cushion that is there if you decide you need it.