Almost any half-geared Shadow Priest can pull aggro in PvE, VE + VT = fail. Before I stopped playing my S.Priest was wearing mostly Badge gear + one or two pieces of T6 and I was either #1 damage or in the top 3 every raid. I was primarily relegated to the healer group for mana regen, while the other DPS'ers (T5/6 mages/locks) got to enjoy constant drum effects and heroisms; I rarely pulled threat on trash and maybe 1-2 times in 50 raids would I pull a boss and that was if everything (damage-wise) was going my way, which rarely happened.
No two players or situations are alike, rating a gearset based on actual situations is near impossible simply because there are too many possible external effects on the recorded data to make it a valid comparison. That's not to say that someone can't review & compare their WWS report to someone elses to gain pointers on doing better.
When it comes down to it, it's all about the skill and intelligence of the individual player. Any fool can mash buttons; but it's the folks that understand cool-down timers, DoT timers, casting speeds, gear/char stats, talent specs, specific boss strategies and how to combine all of those items to play a character to the best they possibly can that will determine their performance in raids, PvP, etc. Some people have the competitive nature to go that far some don't, it becomes glaringly obvious in the stats, and that is why top guilds are so elitist. They have to ensure that they keep the best players for raiding otherwise the players will get bored and will simply leave for a more elitist guild.
Unfortunately in my time playing WoW, while people have always said that I was a really good player I was never able to get into an elite guild to prove my metal against them. Of course I never made a big effort to become their "friend" either. And so it always ended with Mono vs. the World....of Warcraft.