I play a devastation evoker on beta.
I’ve only done quests solo with one exception and that was for an overpowered boss mob on a quest in plains. I rarely have success with large pulls.
My ilv (266) is probably low for my lv (68), but even so I’ve noticed that my health drops fairly fast. Evoker have one defensive as devo, and one fastish aoe heal, while the other self-heal is a spamable cast, but if I pull more than 4 mobs at a time it’s tough to endure the pummeling.
Evoker are definitely intended to be a kite class. They have a good slow, but it’s hard to apply it to large pulls.
Overall, they pump amazing damage, but you better finish the fight before they catch you.
As for facing a single, powerful opponent, it’s much the same. The goal is to keep their hands off you, much like a mage.
Note that this is from someone still learning and leveling the class, so my experience may change at max level, but I doubt I’ll be able to pull large groups or extra scary monsters with no worries until I totally outgear the content.