Archery is actually quite capable of dealing with them as long as you keep a good distance and have some archery skill points. That said I have the same issue on my 2 hander orc but at least you can kill them fairly quickly with a 2 handed weapon. there is the perk that reduces all magic damage done to you by 505 when blocking as well. Another option is to enchant a bow with magicka drain or find a staff to use up all their magicka. Either way i feel like that slow is ridiculously strong except when i use it on my mage haha. Does our version of the spell have the same slow effect?
Well archery is a no go for me, dodging those things is hard since they come at you fast, and even harder to dodge once you are slowed, especially when they are dual casting them.
The biggest problem for me is the slowing effect though, there is no way I can think of to break it. If I could just remove the slow effect with an enrage or a potion, and get close enough to wring their scrawny little caster necks..