(edited by AkkiChan.7164)
Did something happened to Feedback?
A mesmer is more then clones and trickery.
It still blocks the grenade barrage, but the grenades don’t stack up like they did before, because they damage from that was unbalanced. I wasn’t aware that feedback ever blocked the diving bomb, but you should be saving feedback for your normal reflect rotation on that boss anyway and/or saving it for when the grubs spawn.
I don’t think I’ve ever actually fought the spiders in Arah, but it still works just fine on hunters and elementalists.
Also, just a note. At higher fractals, you can’t tank his aoes for arcane thievery anyway. The aoes add agony, and that has to be avoided at all costs.