Most "progressive" metal that you probably had in mind utilizes vocal styles that would make me want to vomit in an instance.
Haha, you have to provide examples. Are you referring to stuff like Pain of Salvation?
Having said that, Gwynbleidd's music, while utilizing certain characteristics of other "progressive" music, is not progressive for the pure sake of being so. I view our music as dark, melodic death/black metal first and foremost.
True, but it's not exactly 'brutal' either. Meaning, it's not at the same intensity of, say, Nile or Morbid Angel. So at some level, you could get away with clean vocals if you wanted to (which you obviously don't want to). The fact that it's a personal preference answers the question.
One thing that's interested me for a while is the overall level and distribution of melody in a song. Bands with all clean vocals tend to have the vast majority of the melody contained in the vocal lines. In contrast, Gothenburg bands can have the same overall level of melody as a pop band, but they shift the melody from the vocals over to the guitars.
Did you know that Mithotyn turned into Falconer because they wanted crowd "sing-a-long" participation? Some bands truly enjoy having their fans sing along with their songs. For the same reason so many melodic death metal bands started using clean vocals (at least in the choruses) just so fans could sing along. Look at Soilwork.
There's definitely something to be said about that point. Being in an arena filled with 70,000 people singing along with Iron Maiden is quite fucking extraordinary. Then again, it's Iron Maiden, and a different style of heavy metal altogether.
I imagine for 'extreme' bands, the energy fed from the crowd is in a moshpit. Or a sea of fists pumping, horns raised.....certainly no 'sing-a-long' in any case.
Each genre has its place.