What each individual considers quality music is most definitely a highly subjective thing.
This is a subjective perception of quality. It does not make quality into a subjective occurrence.
As to black metal being a failure, it was successfully finished in 1994. HLTO had ascended the genre to its highest possible state.
The last 20 years of "black metal" have been 98% music that's BM in name only, with the other 2% quality material that's decent but not comparable to the early 90s. The exception of course is Ildjarn; which is among the best metal ever made, though I'm not sure I would label it black metal.
Also, Ulver and Emperor pioneered nothing.