I agree, MW mist removal is not useful. Its a powerful weapon, but its not a wisplight.
And I agree it should be on a hat or something. Tying it to a weapon reduces choices (well, it would if it were more useful) to pick other weapons that lack it. You always want the weapon selection to be more or less equally viable.

I have found that once you have mastered the ML, beaten the queen etc, you can manage without any light at all fairly well for marble hauling runs. A fire potion trivializes gjall, so even if you can't see it you can back track its shots and still hit them, because stupidly big target. Its not ideal, but if you need carry weight more than visibility... its good enough. You can also drop the torches around your work area. They are so cheap to make.