Executed has Kara/Primal Mooncloth set. Missing 4 enchants (which would give 40 points), has 2 uncommon gems, 3 rare and 4 epic. PM set gives huge healing bonuses but it terribly lacks some stats. For example, first boss in BT requires that you simply must have at least 8500 hp buffed, because breaking shield hits you for 8500. Executed has 6731 unbuffed.
Slipknots has around 11.761 hp unbuffed. He has most of the best Arena gear available, Medallion of the horde instead of some PvE trinket, 1 rare and all other epic gems.
So in your case, Executed would simply
- die after 1 min on Naj'entus OR
- he would have to replace +healing gear with some stamina, because even with buffs he would barely have 8.500 hp, and in that case +healing/MP5 would be more similar to Slipknots
At the end, who would be more useful on that fight: priest who died after 1 min or priest who has less +healing/MP5 but survived the whole fight? Don't get me wrong, PvP gear is NOT something you should bring to raids, there are far better PvE items.
But both of these chars are extremes: Slipknots has great survivability but low healing/MP5, Executed has great healing/MP5 but low survivability. In both cases, as shown on wow-heroes score, characters should expect to perform very well in ZA/SSC/TK but they should both expect BT/MH to be hard-ish. Not impossible, but definitely not easy. Someone in ZA/TK/SSC gear would have higher score then both of them.
I'm really sorry for late reply, I had tons of work