I’m sorry to resurrect an old thread I just randomly saw, but I actually disagree that the HSK 7-9 levels are niche - the common complaint re: the old exam format was that even if you passed HSK 6, if you only followed the exam curriculum you still couldn’t really read many novels in Chinese 
Someone ran multiple novels through a vocabulary frequency analysis tool and it showed that the vocab required for old HSK 6 is only about 50-60% (!!!) of vocab appearing in an average novel. If your Chinese learning goal is being able to fluently consume native-level media the 7-9 levels are necessary.