Did you ever use the arcane protection for anything useful? Did it save you? It shouldn't, arcane bursts happen too often and the scenarios where it might get tricky are somewhat difficult to see when standing behind him I would guess.
I had a Greater Arcane Pot handy for times when it would get dicey but overall they just healed me through it without too many issues.
Our warlock emps tanks are pretty much capped on SR (315). As for warlock aggro, hmm what spell would generate a lot of threat? :o
Shadow bolt + arcane burst with an exploding bug near some healers and then a blizzard hitting a different group of healers at the same time, that's the scenario that usually did it for us :(