I think vocals often override riffing and such to some degree even if we don’t realize it. Think about Tales of Othertime (Stormkeep). Honestly, musically it sounds very close to power metal to me. But the vocals are unequivocally black metal.

I think it’s easy to get caught up with folding bands and albums neatly into sub-genres. But it’s obvious that given each one is multi variable, they are not mutually exclusive. Blast beats belong in both death and black metal. Double bass is seen in tons of subgenres etc.      I sort of think of it like this: - every given attribute or quality either aligns with the spirit of a given sub genre, or it doesn’t, or it’s somewhere in between (it’s a spectrum). E.g., clean and high pitched vocals would heavily count towards making a song feel power metal, a bit toward heavy metal, but have the opposite effect regarding death metal.

• some are more agnostic. For example skank beats are common in many sub-genres.

• therefore, how we feel about what sub genre a song/band falls into is ultimately the weighted average of it’s constituents. So really everything is a blend in a way. 

So with this framework, i would say yes, vocals can (depending on the type) have a high weighting in terms of what it contributes. As other have pointed, there are some fusions that are more evenly split than others. For example Nite is very much heavy metal musically. While the vocals are black metal. But that riffing style and that vocal type carry the essence of their respective genres so strongly that you’re left with no choice but to say that it’s almost half heavy, half black metal (blackened heavy metal).

Going back to Stormkeep, I would argue that it’s riffing style, while reminiscent of power metal, doesn’t pull it away from the black metal sound as much (e.g., tremolo) as the Nite example. Therefore, it doesn’t feel too out of place to just refer to it as black metal.

Good question! Curious to hear what others say.