You only need enough resil to survive an unavoidable situation. It doesn't matter if you stack resil to the cap, if you are caught in a bad position without cds, you'll die. The way I see it, defensive stats are only useful when you take damage, while offensive stats are always useful. The resil/defensive stats threshold("x resil is enough") varies depending on comp, and spec.
I don't know about that. You could easily phrase it another way - defensive stats are always useful, while offensive stats are only useful when you're open long enough to cast a while (not that I necessarily think that, I'm just saying it depends on your point of view). Offensive stats' value deflate considerably if you fight a lot of Beastcleave or TSG, etc. I do agree it depends on comp.
Keep in mind that the most compelling reason to cap resilience is that it will take virtually no effort to do so this season. It has increasing returns till the soft cap, and if you're running the common full PvP gear + exalted AV ring setup that most people are, then by the time you're full Wrathful you're only like 50 resil away from cap anyway even with 0 resil gems.