The key point, which others have alluded to, is that taxonomic ranks are generally entirely arbitrary. If a taxonomist makes up a new rank and other people use it, it is just as valid as any other rank. If a taxonomist decided that what was a subspecies is actually a different family, and other taxonomists go along, well then you’ve got a new family. Other than species, where there are far too many definitions, none of these levels is defined in any way beyond being above and below each other. So the only definition of a subgenus is a taxonomic grouping just below a genus, and just above a section or species group or species. And the only definition of a genus is a taxonomic group just above those things and just below some other things. There is no biology to it, only linguistics and custom.