You can't even see the Gjall "just fine" WITH the wisplight. Much less without it. Now there are certain parts of the Mistlands that don't have much mist, but most of it does. Not killing Yagluth first is just asking to have a terrible experience in the Mistlands. Besides, if you can't kill that guy, you have no business in the ML. Is it possible? I'm sure it is. I'm sure it's possible to beat the Queen naked with only wood arrows and a club and using berries for food. I'd advise against trying it though.