In fact, genomic approaches are more effective at species level and below due to their high resolution power. At high ranks CVTree may be more effective in the sense that it does not require additional work. Suffice it to put genomes in CVTree web server and the branches come out, then compare them with a reference taxonomy.
Why at higher ranks, genomic approaches are more effective? That needs more explanation. And authors should also consider the large benefits of 16S data availability, specially at high ranks (genus and above) where the 16S has good resolution.