This DOES group some kinds of DAT due to their inherently similar nature. TSV and CSV are under the same "SeparatedValue" umbrella, and all of the SFV, MD5, SHA1, etc are under Hashfile because they're nearly identical. This is just the first stage change, making everything static and making them reference the DatFile separately.
BiosSet is the only DatItem type that, by default, has a "Description" field and it was overriding the Machine variant. To make things more consistent, I have renamed this one field since, technically speaking, it is a Machine description, not the DatItem one.