You don't need to be groundbreaking to write good songs or make an album of the year.
The difference between Deafheaven and Ghost is that everyone, including people who don't listen to or follow Metal and would have no way of knowing what's breaking ground in Metal anyway, is hailing Deafheaven as new, innovative, genre-blending geniuses -- when the truth is that what they are doing has already been done.
Ghost, on the other hand, has received nothing but Mercyful Fate comparisons from the start and that's not even really a fair comparison. High-pitched vox, Satanic lyrics, and over the top theatrics to not make you a King clone...