You can set up webs near, but not in, a firewall and mobs can be held and burn.
I personally lucked into a cheap Skyvault shield, so I tend to light a firewall or two and turtle up in it if the mobs don't hit too hard. Much more efficient for the group.
If the mobs hit hard, circle kite as mentioned, and near the melees so they can stand and swing.
My opinion is that at most of the end game, the arcane SHOULD be the one with most of the aggro, it saves everyone resources and things die faster.