This is tantamount to opening Pandora's box. Take for instance bulk and ore carriers, which are two separate categories. Do we then put ore carrying bulk carriers under ore carriers? And put them back again under bulk carriers as soon as we see them carrying soybeans or coal?
Then there is the so called con-bulker, which became popular in the eigthies and are still muddling on? What about the open-hatch bulkers that are now more considered to be general cargo ships, but can take full loads of bulk (probably not ore strengthened though) and containers.
I really have no clear cut answers to this, except that we may end up with one category : Dry Cargo, with three subcategories Fully Cellular container ships, Bulk and ore carriers (anything over 10,000 DWT in there, anything below 10,000 into other drycargo, being the third category.