That video sounded absolutely terrible to me. Under that barrage of drums, the music has no room to breathe or be something.If you single foot your blasts its entirely possible to play Death-Metal with only one pedal, however the lack of the ability to play fast sixteenths with your feet when required can make writing parts tricky if you want the feet to groove and lock in with fast sixteenths on guitar.
During the blast sections George only uses one foot for the kick and uses his other foot for hihat/ribbon crasher.
Alot of early songs fro mold school death metal bands such as Obituary are possible to play with one foots as the double-bass is generally between 110-140bpm sixteenths, so if you have a fast right foot its defintely possible to play with one foot.
Of course, growing up I always considered Black Sabbath as "metal". Nowadays I think Sabbath would be considered light jazz compared to that garbage. The obsession with seeing how fast we can hit stuff makes no sense to me. Music is just something else entirely in my world.